Alloy for r-t-b-based rare earth sintered magnet, process of producing alloy for r-t-b-based rare earth sintered magnet, alloy material for r-t-b-based rare earth sintered magnet, r-t-b-based rare earth sintered magnet, process of producing r-t-b-based rare earth sintered magnet, and motor

ABSTRACT

An alloy for R-T-B-based rare earth sintered magnets which contains R which is a rare earth element; T which is a transition metal essentially containing Fe; a metallic element M containing one or more metals selected from Al, Ga and Cu; B and inevitable impurities, in which R accounts for 13 at % to 15 at %, B accounts for 4.5 at % to 6.2 at %, M accounts for 0.1 at % to 2.4 at %, T accounts for balance, a proportion of Dy in all rare earth elements is in a range of 0 at % to 65 at %, and the following Formula 1 is satisfied, 
       0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1
 
     wherein Dy represents a concentration (at %) of a Dy element, B represents a concentration (at %) of a boron element, and TRE represents a concentration (at %) of all the rare earth elements.

The present invention relates to an alloy for R-T-B-based rare earthsintered magnets, a process of producing the alloy for R-T-B-based rareearth sintered magnets, an alloy material for R-T-B-based rare earthsintered magnets, an R-T-B-based rare earth sintered magnet, a processof producing the R-T-B-based rare earth sintered magnet, and a motor,and particularly to an alloy for R-T-B-based rare earth sintered magnetsand an alloy material for R-T-B-based rare earth sintered magnets whichhave excellent magnetic properties and from which R-T-B-based rare earthsintered magnets that are preferably used for motors can be obtained.

Priority is claimed on Japanese Patent Application No. 2011-151815 filedJul. 8, 2011, Japanese Patent Application No. 2011-229289 filed Oct. 18,2011, Japanese Patent Application No. 2012-060259 filed Mar. 16, 2012,and Japanese Patent Application No. 2012-149560 filed Jul. 3, 2012, thecontents of which are incorporated herein by reference.

BACKGROUND ART

Hitherto, R-T-B-based rare earth sintered magnets (hereinafter,sometimes referred to as “R-T-B-based magnets”) have been used in motorssuch as voice coil motors in hard disc drives and motors for engines inhybrid vehicles or electrical vehicles.

R-T-B-based magnets can be obtained by molding and sintering R-T-B-basedalloy powder primarily containing Nd, Fe and B. Generally, inR-T-B-based alloys, R refers to Nd or a substance containing Nd andother rare earth elements such as Pr, Dy and Tb that substitute some ofNd. T refers to Fe or a substance containing Fe and other transitionelements such as Co and Ni that substitute some of Fe. B refers toboron, and some of B can be substituted by C or N.

The structure of an ordinary R-T-B-based magnet is mainly made up of amain phase made of R₂T₁₄B and an R-rich phase that is present in thegrain boundary of the main phase and has a higher concentration of Ndthan the main phase. The R-rich phase is also called a grain boundaryphase.

In addition, generally, the composition of an R-T-B-based alloy is setso that Nd, Fe and B are in a ratio as close to R₂T₁₄B as possible inorder to increase the proportion of the main phase in the structure ofthe R-T-B-based magent (for example, refer to NPL 1).

In addition, there are cases in which R-T-B-based alloys include anR₂T₁₇ phase. The R₂T₁₇ phase is known as a cause of the degradation ofthe coercive force or squareness of an R-T-B-based magnet (for example,refer to PTL 1). Therefore, in a case in which the R₂T₁₇ phase ispresent in an R-T-B-based alloy, the R₂T₁₇ phase is removed in asintering step of producing an R-T-B-based magent.

In addition, since R-T-B-based magents used in automobile motors areexposed to a high temperature in the motors, a large coercive force(Hcj) is required.

As a technique to improve the coercive forces of R-T-B-based magents,there is a technique that substitutes Nd as R in an R-T-B-based alloywith Dy. However, Dy has biased resources and is thus produced only in alimited amount, and therefore it becomes difficult to stably supply Dy.As a result, studies are being made regarding techniques to improve thecoercive force of an R-T-B-based magnet without increasing the amount ofDy contained in an R-T-B-based alloy.

In order to improve the coercive force (Hcj) of an R-T-B-based magjet,there is a technique that adds metal elements such as Al, Si, Ga and Sn(for example, refer to PTL 2). In addition, it is known that Al and Siare incorporated into an R-T-B-based magnet as inevitable impurities asdescribed in PTL 2. In addition, it is known that, when the amount of Sicontained in an R-T-B-based alloy as an impurity exceeds 5%, thecoercive force of an R-T-B-based magent decreases (for example, refer toPTL 3).

PATENT LITERATURE

-   [PTL 1] Japanese Unexamined Patent Application, First Publication    No. 2007-119882-   [PTL 2] Japanese Unexamined Patent Application, First Publication    No. 2009-231391-   [PTL 3] Japanese Unexamined Patent Application, First Publication    No. H5-112852

Non-Patent Literature

-   [NPL 1] Permanent Magnet-Material Science and Application by Masato    Sagawa, First Edition Second Impression published on Nov. 30, 2008,    pp. 256 to 261

SUMMARY OF INVENTION

However, in the related art, there were cases in which it was notpossible to obtain an R-T-B-based magnet having a sufficiently largecoercive force (Hcj) even when metal elements such as Al, Si, Ga and Snwere added to an R-T-B-based alloy. As a result, it was necessary toincrease the concentration of Dy even when the metallic elements wereadded. Therefore, there was a demand for the supply of an R-T-B-basedalloy from which R-T-B-based magents having a large coercive force couldbe obtained without increasing the amount of Dy contained in theR-T-B-based alloy.

The invention has been made in consideration of the above circumference,and an object of the invention is to provide an alloy for R-T-B-basedrare earth sintered magnets from which R-T-B-based magents having alarge coercive force can be obtained without increasing the amount of Dycontained in the R-T-B-based alloy, an alloy material for R-T-B-basedrare earth sintered magnets, an R-T-B-based rare earth sintered magnetfor which the alloy material for R-T-B-based rare earth sintered magnetsis used, and a process of producing the same.

In addition, another object of the invention is to provide a motor forwhich the R-T-B-based rare earth sintered magnet is used.

The present inventors repeated thorough studies to solve the aboveproblem.

As a result, it was found that, when an R-T-B-based magnet includes amain phase primarily containing R₂Fe₁₄B and a grain boundary containingmore R than the main phase, and the grain boundary phase includes agrain boundary phase (R-rich phase) having a high concentration of rareearth elements which has been thus far known and a grain boundary phase(transition metal-rich phase) having a lower concentration of rare earthelements and a higher concentration of transition metal elements than agrain boundary phase of the related art, it is possible to obtain anR-T-B-based magent having a large coercive force. Furthermore, it wasfound that, as the volume ratio of the transition metal-rich phaseincluded in the R-T-B-based magnet increases, the coercive forceimproves.

In addition, the inventors studied the compositions of an R-T-B-basedalloy as described below in order to develop the effect of the inclusionof Dy that improves the coercive force in an R-T-B-based magentincluding the transition metal-rich phase.

That is, the transition metal-rich phase has a lower concentration ofall atoms of rare earth elements and a higher concentration of Fe atomsthan other grain boundary phases. Therefore, studies have been conductedfor ways to increase the concentration of Fe or to decrease theconcentration of B.

As a result, it was found that the coercive force reached the maximum ata specific concentration of B. Furthermore, it was found that theoptimal concentration of B differs depending on the concentration of Dy.

(1) An alloy for R-T-B-based rare earth sintered magnets containing Rwhich is a rare earth element; T which is a transition metal essentiallycontaining Fe; a metallic element M containing one or more metalsselected from Al, Ga and Cu; B and inevitable impurities, in which Raccounts for 13 at % to 15 at %, B accounts for 4.5 at % to 6.2 at %, Maccounts for 0.1 at % to 2.4 at %, T accounts for balance, a proportionof Dy in all rare earth elements is in a range of 0 at % to 65 at %, andthe following Formula 1 is satisfied.

0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1

In Formula 1, Dy represents the concentration (at %) of a Dy element, Brepresents the concentration (at %) of a boron element, and TRErepresents the concentration (at %) of all the rare earth elements.

(2) The alloy for R-T-B-based rare earth sintered magnets according to(1) containing 0.7 at % to 1.4 at % of the M.

(3) The alloy for R-T-B-based rare earth sintered magnets according to(1) or (2) further containing Si.

(4) The alloy for R-T-B-based rare earth sintered magnets according toany one of (1) to (3), in which an area ratio of a region including anR₂T₁₇ phase is in a range of 0.1% to 50%.

(5) An alloy material for R-T-B-based rare earth sintered magnetsincluding an R-T-B-based alloy containing R which is a rare earthelement; T which is a transition metal essentially containing Fe; B andinevitable impurities, in which R accounts for 13 at % to 15 at %, Baccounts for 4.5 at % to 6.2 at %, T accounts for balance, a proportionof Dy in all rare earth elements is in a range of 0 at % to 65 at %, andthe following Formula 1 is satisfied; and

an additional metal made of a metallic elements M comprising one or moremetals selected from Al, Ga and Cu or an alloy containing the metallicelement M,

in which the alloy material for R-T-B-based rare earth sintered magnetscontains the metallic element M in a range of 0.1 at % to 2.4 at %,

0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1

In Formula 1, Dy represents the concentration (at %) of a Dy element, Brepresents the concentration (at %) of a boron element, and TRErepresents the concentration (at %) of all the rare earth elements.

(6) An alloy material for R-T-B-based rare earth sintered magnetsincluding an R-T-B-based alloy containing R which is a rare earthelement; T which is a transition metal essentially containing Fe; afirst metal comprising one or more metals selected from Al, Ga and Cu; Band inevitable impurities, in which R accounts for 13 at % to 15 at %, Baccounts for 4.5 at % to 6.2 at %, T accounts for balance, a proportionof Dy in all rare earth elements is 0 at % to 65 at %, and the followingFormula 1 is satisfied; and

an additional metal made of a second metal comprising one or more metalsselected from Al, Ga and Cu or an alloy containing the second metal,

in which the alloy material for R-T-B-based rare earth sintered magnetscontains the first metal and the second metal in a range of 0.1 at % to2.4 at % in total,

0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1

In Formula 1, Dy represents a concentration (at %) of a Dy element, Brepresents a concentration (at %) of a boron element, and TRE representsthe concentration (at %) of all the rare earth elements.

(7) The alloy material for R-T-B-based rare earth sintered magnetsaccording to (5) or (6) further containing Si.

(8) The alloy material for R-T-B-based rare earth sintered magnetsaccording to (7), in which a amount of Si in the alloy material forR-T-B-based rare earth sintered magnets is in a range of 0.7 at % to 1.5at %.

(9) The alloy material for R-T-B-based rare earth sintered magnetsaccording to any one of (5) to (8), in which an area ratio of a regionincluding an R₂T₁₇ phase in the R-T-B-based alloy is in a range of 0.1%to 50%.

(10) A process of producing R-T-B-based rare earth sintered magnets, inwhich the alloy for R-T-B-based rare earth sintered magnets according toany one of (1) to (4) or the alloy material for R-T-B-based rare earthsintered magnets according to any one of (5) to (9) is molded andsintered.

(11) The process of producing R-T-B-based rare earth sintered magnetsaccording to (10), in which the sintering is carried out in a range of800° C. to 1200° C., and then a thermal treatment is carried out in arange of 400° C. to 800° C.

(12) The process of producing R-T-B-based rare earth sintered magnetsaccording to (10) or (11), in which a diffusion step of attaching Dymetal or Tb metal, or a Dy compound or a Tb compound to a surface of asintered R-T-B-based magnet and of carrying out a thermal treatment iscarried out.

(13) An R-T-B-based rare earth sintered magnet containing R which is arare earth element; T which is a transition metal essentially containingFe; a metallic element M containing one or more metals selected from Al,Ga and Cu; B and inevitable impurities, in which R accounts for 13 at %to 15 at %, B accounts for 4.5 at % to 6.2 at %, M accounts for 0.1 at %to 2.4 at %, T accounts for balance, a proportion of Dy in all rareearth elements is in a range of 0 at % to 65 at %, the following Formula1 is satisfied,

wherein the R-T-B-based rare earth sintered magnet is made of a sinteredbody including a main phase primarily containing R₂Fe₁₄B and a grainboundary containing more R than the main phase, in which the grainboundary phase includes a phase having a concentration of all atoms ofthe rare earth elements of 70 at % or more and a phase having aconcentration of all the atoms of the rare earth elements in a range of25 at % to 35 at %,

0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1

In Formula 1, Dy represents a concentration (at %) of a Dy element, Brepresents a concentration (at %) of a boron element, and TRE representsthe concentration (at %) of all the rare earth elements.

(14) The R-T-B-based rare earth sintered magnet according to (13)further containing Si.

(15) The R-T-B-based rare earth sintered magnet according to (13) or(14), in which the volume ratio of the phase having a concentration ofall the atoms of the rare earth elements in a range of 25 at % to 35 at% is in a range of 0.005 vol. % to 3 vol. %.

(16) The R-T-B-based rare earth sintered magnet according to any one of(13) to (15), in which a concentration of Dy or Tb on a surface of thesintered magnet is higher than a concentration of Dy or Tb in thesintered magnet.

(17) A motor including the R-T-B-based rare earth sintered magnetaccording to any one of (13) to (16).

(18) An alloy for R-T-B-based rare earth sintered magnets containing Rwhich is a rare earth element; T which is a transition metal essentiallycontaining Fe; a metallic element M containing one or more metalsselected from Al, Ga and Cu; B and inevitable impurities, in which Raccounts for 13 at % to 15 at %, B accounts for 5.0 at % to 6.0 at %, Maccounts for 0.1 at % to 2.4 at %, T accounts for balance, a proportionof Dy in all rare earth elements is in a range of 0 at % to 65 at %, andwherein the alloy for R-T-B-based rare earth sintered magnets includes amain phase primarily containing R₂Fe₁₄B and an alloy grain boundaryphase containing more R than the main phase, and an interval between thealloy grain boundary phases is 3 μm or less.

(19) The alloy for R-T-B-based rare earth sintered magnets according to(18) further containing Si.

(20) The alloy for R-T-B-based rare earth sintered magnets according to(18) or (19), in which a ratio (Fe/B) of an amount of Fe to an amount ofB is in a range of 13 to 16.

(21) The alloy for R-T-B-based rare earth sintered magnets according toany one of (18) to (20), in which B/TRE (B represents a concentration(at %) of a boron element, and TRE represents a concentration (at %) ofall the rare earth elements) is in a range of 0.355 to 0.38.

(22) A process of producing alloys for R-T-B-based rare earth sinteredmagnets including a casting step of casting a molten alloy containing Rwhich is a rare earth element; T which is a transition metal essentiallycontaining Fe; a metallic element M containing one or more metalsselected from Al, Ga and Cu; B and inevitable impurities, in which Raccounts for 13 at % to 15 at %, B accounts for 5.0 at % to 6.0 at %, Maccounts for 0.1 at % to 2.4 at %, T accounts for balance, and aproportion of Dy in all rare earth elements is in a range of 0 at % to65 at % using a strip casting method in which a workpiece is cooledusing a cooling roll, in which, in the casting step, atemperature-holding step of maintaining a cast alloy at a certaintemperature for 10 seconds to 120 seconds while a temperature of thecast alloy decreases from more than 800° C. to lower than 500° C. iscarried out.

(23) The process of producing alloys for R-T-B-based rare earth sinteredmagnets according to (22), in which the molten alloy contains Si.

(24) The process of producing alloys for R-T-B-based rare earth sinteredmagnets according to (22) or (23), in which at least a part of thecasting step is carried out in an atmosphere containing helium.

Further, in the present specification, in order to differentiate thegrain boundary phase of the alloy for R-T-B-based rare earth sinteredmagnets and the grain boundary phase of the R-T-B-based rare earthsintered magnet, the grain boundary phase of the alloy for magnets willbe called the alloy grain boundary phase.

Since the alloy material for R-T-B-based rare earth permanent magnets ofthe invention has a amount of B that satisfies the above (formula 1) andcontains 0.1 at % to 2.4 at % of the metallic element, it is possible tosufficiently ensure the volume ratio of the transition metal-rich phasein an R-T-B-based rare earth permanent magnet formed by molding andsintering the alloy material, and the R-T-B-based rare earth permanentmagnet of the invention having a large coercive force can be obtainedwhile suppressing the amount of Dy.

In addition, since the R-T-B-based rare earth sintered magnet of theinvention has a large coercive force, the R-T-B-based rare earthsintered magnet can be preferably used for motors and the like.

In a case in which the alloy for R-T-B-based rare earth permanentmagnets of the invention contains R which is a rare earth element; Twhich is a transition metal essentially containing Fe; a metallicelement M containing one or more metals selected from Al, Ga and Cu; Band inevitable impurities, in which R accounts for 13 at % to 15 at %, Baccounts for 5.0 at % to 6.0 at %, M accounts for 0.1 at % to 2.4 at %,T accounts for balance, and the proportion of Dy in all the rare earthelements is in a range of 0 at % to 65 at %, the main phase primarilycontaining R₂Fe₁₄B and the alloy grain boundary phase containing more Rthan the main phase are included, and the interval between the alloygrain boundary phases is 3 μm or less, when the alloy is finely groundto 3 μm or less, since the alloy grain boundary has a shape of beingattached to the circumferences of powder, the alloy grain boundary phaseis uniformly distributed among powder, and the grain boundary phase isalso uniformly distributed in a sintered body, and therefore theR-T-B-based rare earth permanent magent of the invention having a largecoercive force can be obtained. As a result, the amount of Dy can besuppressed.

Since the process of producing alloys for R-T-B-based rare earthsintered magnets of the invention is a process in which thetemperature-holding step of maintaining the cast alloy at a certaintemperature for 10 seconds to 120 seconds while the temperature of thecast alloy decreases from more than 800° C. to lower than 500° C. iscarried out in the casting step, it is possible to sufficiently ensurethe volume ratio of the transition metal-rich phase in an R-T-B-basedrare earth permanent magnet formed by molding and sintering the obtainedR-T-B-based alloy, and an R-T-B-based rare earth permanent magnet havinga large coercive force can be obtained while suppressing the amount ofDy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view in which a relationship between B/TRE (B represents aconcentration (at %) of a boron element, and TRE represents aconcentration (at %) of all the rare earth elements) and Hcj (coerciveforce) of a sintered magnet manufactured using an alloy having Dy=0 at %is plotted.

FIG. 2 is a view in which the relationship between B/TRE (B represents aconcentration (at %) of a boron element, and TRE represents aconcentration (at %) of all the rare earth elements) and Hcj (coerciveforce) of a sintered magnet manufactured using an alloy having Dy≈3.8 at% is plotted.

FIG. 3 is a view in which the relationship between B/TRE (B represents aconcentration (at %) of a boron element, and TRE represents aconcentration (at %) of all the rare earth elements) and Hcj (coerciveforce) of a sintered magnet manufactured using an alloy having Dy≈8.3 at% is plotted.

FIG. 4 is a view in which the relationship between a concentration of Dyand B/TRE (B represents a concentration (at %) of a boron element, andTRE represents a concentration (at %) of all the rare earth elements) ata point at which the coercive force reaches the maximum is plotted.

FIG. 5 is an R-T-B ternary phase diagram.

FIG. 6 is a backscattered electron image of a cross-section of Alloy F.

FIG. 7 is a view of an enlarged region in which an R₂T₁₇ phase isgenerated.

FIG. 8 is a microscope photograph of an R-T-B-based magnet and abackscattered electron image of an R-T-B-based magnet of ExperimentExample 9.

FIG. 9 is a microscope photograph of an R-T-B-based magnet and abackscattered electron image of an R-T-B-based magnet of ExperimentExample 6.

FIG. 10( a) is a microscope photograph of an R-T-B-based magnet of theinvention and a backscattered electron image of an R-T-B-based magnet ofExperiment Example 23. FIG. 10( b) is a schematic view for describingthe microscope photograph of the R-T-B-based magnet illustrated in FIG.10( a).

FIG. 11 is a schematic front view illustrating an example of anapparatus which is used to produce an alloy.

FIG. 12( a) is a graph illustrating a relationship between a distancebetween alloy grain boundary phases and a concentration of B, FIG. 12(b) is a graph illustrating a relationship between a distance betweenalloy grain boundary phases and B/TRE, and FIG. 12( c) is a graphillustrating a relationship between a distance between alloy grainboundary phases and Fe/B.

FIG. 13( a) is a microscope photograph of a cross-section of a thin castalloy piece for which Fe/B is 15.5, and FIG. 13( b) is a microscopephotograph of a cross-section of a thin cast alloy piece for which Fe/Bis 16.4.

FIG. 14 is a graph illustrating distances between alloy grain boundaryphases in Experiment Example 35 and distances between alloy grainboundary phases in Experiment Example 36.

FIG. 15 illustrates graphs showing relationships between an elapsed timefor a produced cast alloy to reach 50° C. from 1200° C. and atemperature. FIG. 15( a) illustrates the temperatures against theelapsed times in a range of 0 seconds to 1 second, FIG. 15( b)illustrates the temperatures against the elapsed times in a range of 0seconds to 250 seconds, and FIG. 15( c) illustrates the temperaturesagainst the elapsed times in a range of 0 seconds to 700 seconds.

FIG. 16( a) is a graph illustrating coercive forces (Hcj) of R-T-B-basedmagnets of Experiment Examples 37 to 40, FIG. 16( b) is a graphillustrating remanence (Br) of the R-T-B-based magnets of ExperimentExamples 37 to 40, and FIG. 16( c) is a graph illustrating arelationship between the remanence (Br) and coercive forces (Hcj) of theR-T-B-based magnets of Experiment Examples 37 to 40.

FIG. 17( a) is a graph illustrating second quadrants of hysteresiscurves of Experiment Examples 47 and 48 measured using a BH curvetracer, and FIG. 17( b) is a graph illustrating second quadrants ofhysteresis curves of Experiment Examples 49 and 50 measured using a BHcurve tracer. The vertical axis indicates magnetization and thehorizontal axis indicates magnetic fields H.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the invention will be described in detail.

First Embodiment

“Alloy for R-T-B-Based Rare Earth Sintered Magnets”

An alloy for R-T-B-based rare earth sintered magnets of the presentembodiment (hereinafter abbreviated to “R-T-B-based alloy”) is an alloyused to produce an R-T-B-based rare earth sintered magnet (hereinafterabbreviated to “R-T-B-based magnet”) of the invention formed by moldingand sintering a sintered body including a main phase primarilycontaining R₂Fe₁₄B and a grain boundary phase containing more R than themain phase, in which the grain boundary phase includes an R-rich phaseand a transition metal-rich phase that is a grain boundary phase havinga lower concentration of rare earth elements and a higher concentrationof transition metal elements than the R-rich phase.

In the embodiment, the R-rich phase is a phase in which theconcentration of all atoms of R which is rare earth elements is 70 at %or more. The transition metal-rich phase is a phase in which theconcentration of all atoms of the rare earth element R is in a range of25 at % to 35 at %. The transition metal-rich phase preferably contains50 at % to 70 at % of T which is a transition metal essentiallycontaining Fe.

The R-T-B-based alloy of the embodiment is an R-T-B-based alloycontaining R which is a rare earth element, T which is a transitionmetal essentially containing Fe, a metallic element M containing one ormore metals selected from Al, Ga and Cu, B and inevitable impurities, inwhich R accounts for 13 at % to 15 at %, B accounts for 4.5 at % to 6.2at %, M accounts for 0.1 at % to 2.4 at %, T accounts for balance, andthe following Formula 1 is satisfied. In addition, the R-T-B-based alloyof the embodiment is an alloy in which the proportion of Dy in all rareearth elements is in a range of 0 at % to 65 at %.

0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1

In Formula 1, Dy represents a concentration (at %) of a Dy element, Brepresents a concentration (at %) of a boron element, and TRE representsa concentration (at %) of all the rare earth elements.

When the amount of R contained in the R-T-B-based alloy is less than 13at %, the coercive force of an R-T-B-based magnet obtained using thealloy becomes insufficient. In addition, when the amount of R exceeds 15at %, the remanence of an R-T-B-based magnet obtained using the alloybecomes low, and the magnet becomes unsuitable for magnets.

The amount of Dy in all the rare earth elements in the R-T-B-based alloyis set in a range of 0 at % to 65 at %. In the embodiment, since theinclusion of the transition metal-rich phase improves the coerciveforce, the R-T-B-based alloy may not contain Dy, and even in a case inwhich the R-T-B-based alloy contains Dy, a large effect that improvesthe coercive force can be sufficiently obtained at an amount of 65 at %or less.

Examples of rare earth elements other than Dy in the R-T-B-based alloyinclude Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb andLu, and, among the above, Nd, Pr and Tb are particularly preferable. Inaddition, R in the R-T-B-based alloy preferably contains Nd as a maincomponent.

In addition, B contained in the R-T-B-based alloy is boron, and some ofB can be substituted by C or N. The amount of B is in a range of 4.5 at% to 6.2 at %, and satisfies the above Formula 1. The amount of B ismore preferably in a range of 4.8 at % to 5.5 at %. When the amount of Bcontained in the R-T-B-based alloy is less than 4.5 at %, the coerciveforce of an R-T-B-based magnet obtained using the alloy becomesinsufficient. When the amount of B is beyond the range of the aboveFormula 1, the generation amount of the transition metal-rich phasebecomes insufficient, and the coercive force does not sufficientlyimprove.

The R-T-B-based alloy of the embodiment includes a main phase primarilycontaining R₂Fe₁₄B and an alloy grain boundary phase containing more Rthan the main phase. The alloy grain boundary phase can be observedusing a backscattered electron image of an electronic microscope. Thealloy grain boundary phase may contain, substantially, only R or containR-T-M.

In the R-T-B-based alloy of the embodiment, in order to set the intervalbetween the alloy grain boundary phases to 3 μm or less, the amount of Bcontained in the R-T-B-based alloy is set in a range of 5.0 at % to 6.0at %. When the amount of B is set in the above range, the grain diameterof an alloy structure decreases so that grindability improves, and thegrain boundary phase is uniformly distributed in an R-T-B-based magnetproduced using the alloy so as to obtain an excellent coercive force. Inorder to obtain a fine alloy structure having superior grindability andan interval between the alloy grain boundary phases of 3 μm or less, theamount of B is preferably set to 5.5 at % or less. However, in a case inwhich the amount of B contained in the R-T-B-based alloy is less than5.0 at %, the interval between adjacent alloy grain boundary phases inthe R-T-B-based alloy abruptly increases, and it becomes difficult toobtain a fine alloy structure having an interval between the alloy grainboundary phases of 3 μm or less. In addition, as the amount of Bcontained in the R-T-B-based alloy increases, the interval betweenadjacent alloy grain boundary phases in the R-T-B-based alloy abruptlyincreases, and alloy grains become large. In addition, when the amountof B becomes excessive, a B-rich phase is included in a sintered magnet.Therefore, in a case in which the amount of B exceeds 6.0 at %, there isa concern that the coercive force of an R-T-B-based magnet producedusing the alloy may become insufficient.

In addition, in order to decrease the grain diameter of the alloystructure so as to improve the coercive force of an R-T-B-based magnetproduced using the alloy, the ratio (Fe/B) of the amount of Fe to theamount of B contained in the R-T-B-based alloy is preferably in a rangeof 13 to 16. In addition, in a case in which Fe/B is in a range of 13 to16, the generation of the transition metal-rich phase is effectivelyaccelerated in a step of producing R-T-B-based alloys and/or a step ofproducing R-T-B-based magnets. However, when Fe/B exceeds 16, theinterval between adjacent alloy grain boundary phases in the R-T-B-basedalloy abruptly increases, and it becomes difficult to obtain a finealloy structure having an interval between the alloy grain boundaryphases of 3 μm or less.

In addition, when Fe/B becomes less than 13, as Fe/B decreases, theinterval between adjacent alloy grain boundary phases in the R-T-B-basedalloy increases, and alloy grains become large. Therefore, in a case inwhich Fe/B is less than 13, there is a concern that the coercive forceof an R-T-B-based magnet produced using the alloy may becomeinsufficient.

In addition, in order to decrease the grain diameter of the alloystructure so as to improve the coercive force of an R-T-B-based magnetproduced using the alloy, B/TRE is preferably set in a range of 0.355 to0.38. B/TRE is more preferably 0.36 or less so as to obtain a fine alloystructure having superior grindability and an interval between the alloygrain boundary phases of 3 μm or less. In a case in which B/TRE is lessthan 0.355, the interval between adjacent alloy grain boundary phases inthe R-T-B-based alloy abruptly increases, and it becomes difficult toobtain a fine alloy structure having an interval between the alloy grainboundary phases of 3 μm or less. In addition, as B/TRE increases, theinterval between adjacent alloy grain boundary phases in the R-T-B-basedalloy increases, and alloy grains become large. Therefore, in a case inwhich B/TRE exceeds 0.38, there is a concern that the coercive force ofan R-T-B-based magnet produced using the alloy may become insufficient.

In addition, T contained in the R-T-B-based alloy is a transition metalessentially containing Fe. As transition metals other than Fe containedin T of the R-T-B-based alloy, a variety of elements belonging to Groups3 to 11 can be used. In a case in which the R-T-B-based alloy containsCo in addition to Fe, the curie temperature (Tc) can be improved, whichis preferable.

FIG. 1 is a view in which the relationship between B/TRE (B represents aconcentration (at %) of a boron element, and TRE represents aconcentration (at %) of all the rare earth elements) and Hcj (coerciveforce) of a sintered magnet manufactured using an alloy having Dy=0 at %is plotted. In FIG. 1, the coercive force reaches the maximum whenB/TRE=0.35.

FIG. 2 is a view in which the relationship between B/TRE (B represents aconcentration (at %) of a boron element, and TRE represents aconcentration (at %) of all the rare earth elements) and Hcj (coerciveforce) of a sintered magnet manufactured using an alloy having Dy≈3.8 at% is plotted. In FIG. 2, the coercive force reaches the maximum whenB/TRE=0.37.

FIG. 3 is a view in which the relationship between B/TRE (B represents aconcentration (at %) of a boron element, and TRE represents aconcentration (at %) of all the rare earth elements) and Hcj (coerciveforce) of a sintered magnet manufactured using an alloy having Dy≈8.2 at% is plotted. In FIG. 3, the coercive force reaches the maximum whenB/TRE=0.39.

When the relationship between the concentration of Dy and B/TRE at apoint at which the coercive force reaches the maximum is plotted, therelationship becomes as illustrated in FIG. 4. From the straight line inFIG. 4, the following formula is derived.

B/TRE=0.0049Dy+0.35  Formula 2

From FIGS. 2 and 3, it is found that the width of B/TRE in which thecoercive force decreases from the maximum to less than 90% of themaximum value is outside a range of B/TRE at which the coercive forcereaches the maximum±0.01. That is, in a range of the above (Formula2)−0.01 to the above (Formula 2)+0.01, a coercive force that is equal toor larger than 90% of the maximum coercive force can be obtained. Withan assumption that the above range is an appropriate B/TRE, theappropriate range of B/TRE is represented by the following Formula 1.

0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1

An alloy that satisfies the above Formula 1 has a higher concentrationof Fe and a lower concentration of B than an R-T-B-based alloy of therelated art. FIG. 5 is an R-T-B ternary phase diagram. In FIG. 5, thevertical axis indicates the concentration of B, and the horizontal axisindicates the concentration of Nd. FIG. 5 illustrates that, as theconcentration of B and the concentration of Nd decrease, theconcentration of Fe increases. Generally, an alloy with a composition(for example, a composition indicated using a black Δ in FIG. 5) in acolored region is cast, thereby manufacturing an R-T-B-based magnet madeup of the main phase and the R-rich phase. However, the compositions ofthe R-T-B-based alloys of the invention which satisfy the above Formula1 are in a region on the low-B concentration side of the above region asillustrated using O in FIG. 5.

When an R-T-B-based alloy that satisfies the above Formula 1 ismanufactured, an R₂T₁₇ phase is easily generated. The R₂T₁₇ phase isknown as a cause of the degradation of the coercive force or squarenessof an R-T-B-based magnet, and, generally, an R-T-B-based alloy isproduced under a condition in which the R₂T₁₇ phase is not generated.However, in the invention, the R₂T₁₇ phase is considered to serve as araw material for the transition metal-rich phase in a step of producingR-T-B-based alloys and/or a step of producing R-T-B-based magnets.

In the R-T-B-based alloy of the invention, the area ratio of a regionincluding the R₂T₁₇ phase is preferably in a range of 0.1% to 50%, andmore preferably in a range of 0.1% to 25%. In a case in which the arearatio of a region including the R₂T₁₇ phase is in the above range, thegeneration of the transition metal-rich phase is effectivelyaccelerated, and an R-T-B-based magnet which sufficiently includes thetransition metal-rich phase and has a large coercive force can beobtained. When the area ratio of a region including the R₂T₁₇ phase is50% or more, it is not possible to fully consume the R₂T₁₇ phase in astep of producing R-T-B-based magnets, and there are cases in which thecoercive force or squareness of an R-T-B-based magnet degrades.

Furthermore, in the R-T-B-based alloy of the embodiment, in a case inwhich the area ratio of a region including the R₂T₁₇ phase is in a rangeof 0.1% to 50%, excellent grindability can be obtained. Since the R₂T₁₇phase is more brittle than an R₂T₁₄B phase, in a case in which theR-T-B-based alloy of the invention includes a region including the R₂T₁₇phase at an area ratio in a range of 0.1% to 50%, the alloy is easilyground, and thus it is possible to make the alloy into fine grains witha grain diameter of approximately 2 μm.

The area ratio of a region including the R₂T₁₇ phase is obtained bymicroscopically observing a cross-section of a thin cast alloy piecewhich will become an R-T-B-based alloy. Specifically, the area ratio isobtained in the following order.

A thin cast alloy piece is embedded in a resin, cut in the thicknessdirection of the thin cast alloy piece, mirror-polished, and then goldor carbon is deposited to supply a conductive property, therebypreparing an observation specimen. A backscattered electron image of thespecimen is photographed using a scanning electron microscope at amagnification of 300 times or 350 times.

FIG. 6 illustrates a backscattered electron image of a cross-section ofAlloy F described in Table 1 photographed at a magnification of 350times as an example. In the image, a gray R₂T₁₄B phase and whiteline-shaped R-rich phases are observed. Additionally, there are regionsin which dot-shaped R-rich phases are observed (regions surrounded bywhite lines). In the present application, the above region will becalled a region including the R₂T₁₇ phase. The ratio of the area of theregion to a photograph of the cross-section will be called the arearatio of the region including the R₂T₁₇ phase.

FIG. 7 is a high-magnification photograph of a region in which the R₂T₁₇phase is generated. When FIG. 7 is strongly contrasted, it is found thatblack dot-shaped R₂T₁₇ phases (2-17 phases), white R-rich phases andgray main phases (2-14-1 phases) are generated in the region in whichthe R₂T₁₇ phase is generated.

The metallic element M contained in the R-T-B-based alloy of theembodiment is assumed to accelerate the generation of the transitionmetal-rich phase in a step of temporarily slowing the cooling rate of athin cast alloy piece after casting which is carried out when producingthe R-T-B-based alloy (temperature retention step of a cast alloydescribed below) or during sintering and a thermal treatment forproducing the R-T-B-based magnet. The metallic element M contains one ormore metals selected from Al, Ga and Cu, and is contained in a range of0.1 at % to 2.4 at % in the R-T-B-based alloy.

Since the R-T-B-based alloy of the embodiment contains 0.1 at % to 2.4at % of the metallic element M, when the R-T-B-based alloy is sintered,an R-T-B-based magnet including the R-rich phase and the transitionmetal-rich phase can be obtained.

One or more metals selected from Al, Ga and Cu, which are contained inthe metallic element M, accelerate the generation of the transitionmetal-rich phase in the temperature retention step of the cast alloy orduring the sintering or thermal treatment of the R-T-B-based magnetwithout adversely affecting other magnetic properties, therebyeffectively improving the coercive force (Hcj).

When the amount of the metallic element M is less than 0.1 at %, thereis a concern that the effect that accelerates the generation of thetransition metal-rich phase may not be sufficiently developed such thatthe transition metal-rich phase is not formed in the R-T-B-based magnetand the coercive force (Hcj) of the R-T-B-based magnet cannot besufficiently improved. In addition, when the amount of the metallicelement M exceeds 2.4 at %, magnetic properties such as the remanence(Br) of the R-T-B-based magnet or the maximum energy product (BHmax)degrade. The amount of the metallic element M is more preferably in arange of 0.7 at % to 1.4 at %.

In a case in which the R-T-B-based alloy contains Cu, the concentrationof Cu is preferably in a range of 0.07 at % to 1 at %. In a case inwhich the concentration of Cu is less than 0.07 at %, the magnet becomesdifficult to sinter.

In addition, in a case in which the concentration of Cu exceeds 1 at %,the remanence (Br) of the R-T-B-based magnet degrades, which is notpreferable.

The R-T-B-based alloy of the embodiment may further contain Si inaddition to R which is a rare earth element, T which is a transitionmetal essentially containing Fe, a metallic element M containing one ormore metals selected from Al, Ga and Cu, and B. In a case in which theR-T-B-based alloy contains Si, the amount of Si is preferably in a rangeof 0.7 at % to 1.5 at %. When the R-T-B-based alloy contains Si in theabove range, the coercive force further improves. When the amount of Siis less than 0.7 at % or more than 1.5 at %, the effect of the inclusionof Si degrades.

In addition, when the total concentration of oxygen, nitrogen and carboncontained in the R-T-B-based alloy is high, in a step of sintering theR-T-B-based magnet described below, the rare earth element R bonds withthe above elements, which leads to the consumption of the rare earthelement R. Therefore, out of the rare earth element R contained in theR-T-B-based alloy, the amount of the rare earth element R that can beused as a raw material for the transition metal-rich phase in thethermal treatment of the R-T-B-based magnet obtained by sintering thealloy decreases. As a result, there is a concern that the generationamount of the transition metal-rich phase may decrease and the coerciveforce of the R-T-B-based magnet may become insufficient. Therefore, inthe embodiment, the total concentration of oxygen, nitrogen and carboncontained in the R-T-B-based alloy is preferably 0.5 wt % or less. Whenthe total concentration is set to the above concentration or less, theconsumption of the rare earth element R is suppressed, and the coerciveforce (Hcj) can be effectively improved.

“Process of Producing the R-T-B-Based Alloy”

The R-T-B-based alloy of the invention is obtained as follows. Forexample, an approximately 1450° C.-hot molten alloy with a predeterminedcomposition is cast using, for example, a strip cast (SC) method,thereby producing a thin cast alloy piece. At this time, a treatment(temperature retention step) in which the cooling rate of the thin castalloy piece after the casting is temporarily slowed in a range of 700°C. to 900° C. so as to accelerate the diffusion of the components in thealloy may be carried out.

After that, the obtained thin cast alloy piece is cracked using ahydrogen decrepitation method or the like, and ground using a grinder,thereby obtaining an R-T-B-based alloy.

In the embodiment, a process in which an R-T-B-based alloy is producedusing a production apparatus illustrated in FIG. 11 will be described asan example of a process of producing the R-T-B-based alloy of theinvention.

(Apparatus for Producing the Alloy)

FIG. 11 is a schematic front view illustrating an example of anapparatus used to produce the alloy.

The apparatus used to produce the alloy 1 illustrated in FIG. 11includes a casting apparatus 2, a crushing apparatus 21, a heatingapparatus 3 disposed below the crushing apparatus 21 and a storagecontainer 4 disposed below the heating apparatus 3.

The crushing apparatus 21 is an apparatus that crushes a cast alloy lumpthat is cast using the casting apparatus 2, thereby preparing thin castalloy pieces. As illustrated in FIG. 11, a hopper 7 that guides the thincast alloy pieces to an openable stage group 32 in the heating apparatus3 is provided between the crushing apparatus 21 and the openable stagegroup 32.

The heating apparatus 3 is made up of a heating heater 31 and acontainer 5. The container 5 includes the storage container 4 and theopenable stage group 32 installed above the storage container 4. Theopenable stage group 32 is made up of a plurality of openable stages 33.The openable stages 33 mount the thin cast alloy pieces supplied fromthe crushing apparatus 21 when in a close state, and send the thin castalloy pieces to the storage container 4 when in an open state.

In addition, the production apparatus 1 includes a belt conveyor 51(moving apparatus) that freely moves the container 5 so that thecontainer 5 can be moved in the horizontal direction in FIG. 11 usingthe belt conveyor 51.

In addition, the production apparatus 1 illustrated in FIG. 11 includesa chamber 6. The chamber 6 includes a casting chamber 6 a and a heatretention and storage chamber 6 b which is installed below the castingchamber 6 a and communicated with the casting chamber 6 a. The castingchamber 6 a accommodates the casting apparatus 2, and the heat retentionand storage chamber 6 b accommodates the heating apparatus 3.

In order to produce an R-T-B-based alloy in the embodiment, first, anapproximately 1450° C.-hot molten alloy with a predetermined compositionis prepared in a melting apparatus, not illustrated. Next, the obtainedmolten alloy is supplied to a cooling roll 22 made up of a copper rollfor water cooling in the casting apparatus 2 using a tundish, notillustrated, and solidified, thereby preparing a cast alloy. After that,the cast alloy is detached from the cooling roll 22, and crushed betweencrushing rolls in the crushing apparatus 21, thereby preparing thin castalloy pieces.

The crushed thin cast alloy pieces are made to pass through the hopper7, and stacked on the openable stages 33 in a “close” state in theopenable stage group 32 disposed below the hopper 7. The thin cast alloypieces stacked on the openable stages 33 are heated using the heatingheater 31.

In the embodiment, a temperature retention step in which the producedcast alloy that is hotter than 800° C. is maintained at a certaintemperature for 10 seconds to 120 seconds until the temperature of thecast alloy reaches below 500° C. is carried out. In the embodiment, thethin cast alloy pieces start to be heated using the heating heater 31from when the thin cast alloy pieces in a temperature range of 800° C.to 500° C. are supplied to the openable stages 33 and stacked on theopenable stages 33. Then, the temperature retention step in which thecast alloy is maintained at a certain temperature for 10 seconds to 120seconds begins.

After a predetermined time elapses, the openable stages 33 are switchedinto an “open” state, and the thin cast alloy pieces stacked on theopenable stages 33 are dropped into the storage container 4. Then, heatfrom the heating heater 31 cannot reach the thin cast alloy pieces, thethin cast alloy pieces start to be cooled again, and the temperatureretention step ends.

In a case in which the temperature retention step is carried out, it isassumed that, among the elements contained in the cast alloy, thecomponent switching between the metallic element M containing one ormore metals selected from Al, Ga and Cu; and B is accelerated due to therearrangement of elements moving in the cast alloy. Then, it is assumedthat some of B contained in a region which serves as the alloy grainboundary phase moves to the main phase, and some of the metallic elementM contained in a region which serves as the main phase moves to thealloy grain boundary phase. As a result, it is assumed that theintrinsic magnetic properties of the main phase cannot be exhibited, andtherefore the coercive force of an R-T-B-based magnet obtained using thealloy increases.

In a case in which the temperature of the cast alloy exceeds 800° C. inthe temperature retention step, there is a concern that the alloystructure may coarsen. In addition, in a case in which the time exceeds120 seconds during which the cast alloy is maintained at a certaintemperature, there are cases in which productivity is adverselyaffected.

In addition, in a case in which the temperature of the cast alloy islower than 500° C. in the temperature retention step or a case in whichthe time is less than 10 seconds during which the cast alloy ismaintained at a certain temperature, there are cases in which the effectof the temperature retention step that rearranges elements cannot besufficiently obtained.

Meanwhile, in the embodiment, the temperature retention step is carriedout using a process in which the thin cast alloy pieces which are in atemperature range of 800° C. to 500° C. and stacked on the openablestages 33 are heated using the heating heater 31, but the process forcarrying out the temperature retention step is not limited as long asthe cast alloy hotter than 800° C. can be maintained at a certaintemperature for 10 seconds to 120 seconds until the temperature of thecast alloy reaches below 500° C.

In addition, in the process of producing the R-T-B-based alloy of theembodiment, a reduced-pressure atmosphere of an inert gas is preferablyformed in the chamber 6 in which the R-T-B-based alloy is produced.Furthermore, in the embodiment, at least a part of the casting step ispreferably carried out in an atmosphere containing helium. Helium has abetter capability that dissipates heat from the cast alloy than argon,and it is possible to easily increase the cooling rate of the castalloy.

Examples of the process in which at least a part of the casting step iscarried out in an atmosphere containing helium include a process inwhich helium is supplied as the inert gas at a predetermined flow rateinto the casting chamber 6 a in the chamber 6. In this case, since anatmosphere containing helium is formed in the casting chamber 6 a, it ispossible to efficiently cool the surfaces of the cast alloy, which iscast using the casting apparatus 2 and quenched using the cooling roll22, which are not in contact with the cooling roll 22. Therefore, thecooling rate of the cast alloy increases, the grain diameter of thealloy structure decreases, the crushability becomes excellent, a finealloy structure having an interval between the alloy grain boundaryphases of 3 μm or less is easily obtained, and the coercive force of anR-T-B-based magnet produced using the alloy can be improved. Inaddition, in a case in which an atmosphere containing helium is formedin the casting chamber 6 a, since the cooling rate of the cast alloyincreases, it is possible to easily set the temperature of the thin castalloy pieces stacked on the openable stages 33 to 800° C. or lower.

In addition, in the process of producing the R-T-B-based alloy of theembodiment, the thin cast alloy pieces which have been subjected to thetemperature retention step are preferably cooled in an atmospherecontaining helium. Then, since the cooling rate of the thin cast alloypieces, which are the cast alloy that has been subjected to thetemperature retention step, increases, the alloy structure is furtherminimized, and a fine alloy structure which has excellent crushabilityand an interval between the alloy grain boundary phases of 3 μm or lessis easily obtained. Examples of a process for cooling the thin castalloy pieces that have been subjected to the temperature retention stepin an atmosphere containing helium include a process in which helium issupplied at a predetermined flow rate into the storage container 4 thataccommodates the thin cast alloy pieces dropped from the openable stages33.

Meanwhile, in the embodiment, a case in which the R-T-B-based alloy isproduced using the SC method has been described, but the R-T-B-basedalloy used in the invention is not limited to the alloy produced usingthe SC method. For example, the R-T-B-based alloy may be cast using acentrifugal casting method, a book mold method or the like.

The hydrogen decrepitation method is carried out in an order in which,for example, hydrogen is absorbed in the thin cast alloy pieces at roomtemperature, the thin cast alloy pieces are thermally treated inhydrogen at a temperature of approximately 300° C., then, the pressureis reduced so as to desorb hydrogen, and then the thin cast alloy piecesare thermally treated at a temperature of approximately 500° C., therebyremoving hydrogen in the thin cast alloy pieces. In the hydrogendecrepitation method, since the volume of the thin cast alloy piecesthat have absorbed hydrogen increases, a number of cracks are easilygenerated in the alloy, and the alloy is cracked.

In addition, jet milling or the like is used as a process for grindingthe hydrogen-decrepitated thin cast alloy pieces. Thehydrogen-decrepitated thin cast alloy pieces are put into a jet millcrusher, and finely crushed to an average grain diameter in a range of 1μm to 4.5 μm using high-pressure, for example, 0.6 MPa nitrogen, therebypreparing powder. As the average grain size of the powder decreases, thecoercive force of a sintered magnet can be further improved. However,when the grain size is not significantly decreased, the powder surfacesare easily oxidized, and, conversely, the coercive force decreases.

“Process of Producing the R-T-B-Based Rare Earth Sintered Magnets”

Next, a process of producing an R-T-B-based magnet using the R-T-B-basedalloy of the embodiment obtained in the above manner will be described.

Examples of the process of producing an R-T-B-based magnet of theembodiment include a process in which 0.02 mass % to 0.03 mass % of zincstearate is added to the powder of the R-T-B-based alloy of theembodiment as a lubricant, the powder is press-molded using a machinefor molding in a transverse magnetic field or the like, sintered in avacuum, and then thermally treated.

In a case in which the powder is sintered in a range of 800° C. to 1200°C., and more preferably in a range of 900° C. to 1200° C., and thenthermally treated in a range of 400° C. to 800° C., the transitionmetal-rich phase is more easily generated in the R-T-B-based magnet, andan R-T-B-based magnet having a larger coercive force can be obtained.

In the embodiment, when the above Formula 1 is satisfied, the R₂T_(i7)phase is generated in the R-T-B-based alloy. The R₂T₁₇ phase is assumedto be used as a raw material for the transition metal-rich phase in thethermal treatment of an R-T-B-based magnet obtained by sintering theR-T-B-based alloy.

The thermal treatment after the sintering may be carried out just onceor twice or more. For example, in a case in which the thermal treatmentafter the sintering is carried out just once, the thermal treatment ispreferably carried out in a range of 500° C. to 530° C. In addition, ina case in which the thermal treatment after the sintering is carried outtwice, the thermal treatment is preferably carried out at twotemperatures in a range of 530° C. to 800° C. and in a range of 400° C.to 500° C.

In a case in which the thermal treatment is carried out at twotemperatures, since the generation of the transition metal-rich phase isaccelerated as described below, it is assumed that an R-T-B-based magnethaving a superior coercive force can be obtained.

In a case in which the thermal treatment is carried out at twotemperatures, in the first thermal treatment in a range of 530° C. to800° C., the R-rich phase turns into a liquid phase and rotates aroundthe main phase (2-14-1 phase). Then, in the second thermal treatment ina range of 400° C. to 500° C., a reaction among the R-rich phase, the2-17 phase (R₂T₁₇ phase) and the metallic element M is accelerated, andthe generation of the transition metal-rich phase is accelerated.

In the process of producing the R-T-B-based magnet of the embodiment,since an alloy having a amount of B which satisfies the above Formula 1and 0.1 at % to 2.4 at % of the metallic element M is used as theR-T-B-based alloy, the R-T-B-based magnet of the invention which is madeof a sintered body including a main phase 11 h primarily containingR₂Fe₁₄B and a grain boundary phase containing more R than the mainphase, in which the grain boundary phase includes an R-rich phase havinga concentration of all atoms of rare earth elements of 70 at % or moreand a transition metal-rich phase having a concentration of all atoms ofrare earth elements in a range of 25 at % to 35 at % is obtained.

Furthermore, when the kind or use amount of the metallic elementcontained in the R-T-B-based alloy of the embodiment, the volume ratioof the region including the R₂T₁₇ phase, and the composition of theR-T-B-based alloy are adjusted in the above ranges, and the conditionssuch as the sintering temperature or the thermal treatment aftersintering are adjusted, it is possible to easily adjust the volume ratioof the transition metal-rich phase in the R-T-B-based magnet to apreferable range of 0.005 vol % to 3 vol %.

In addition, an R-T-B-based magnet which suppresses the amount of Dy andhas a predetermined coercive force suitable for use can be obtained byadjusting the volume ratio of the transition metal-rich phase in theR-T-B-based magnet.

In addition, the effect that improves the coercive force (Hcj), which isobtained in the R-T-B-based magnet of the invention, is assumed toresult from the formation of the transition metal-rich phase containinga high concentration of Fe in the grain boundary phase. The volume ratioof the transition metal-rich phase included in the R-T-B-based magnet ofthe invention is preferably 0.005 vol % to 3 vol %, and more preferably0.1 vol % to 2 vol %.

When the volume ratio of the transition metal-rich phase is in the aboverange, the effect of the inclusion of the transition metal-rich phase inthe grain boundary phase that improves the coercive force can be moreeffectively obtained. In contrast to what has been described above, whenthe volume ratio of the transition metal-rich phase is less than 0.1 vol%, there is a concern that the effect that improves the coercive force(Hcj) may become insufficient. In addition, when the volume ratio of thetransition metal-rich phase exceeds 3 vol %, adverse effects on themagnetic properties, such as the degradation of the remanence (Br) orthe maximum energy product ((BH)max), are caused, which is notpreferable.

The concentration of Fe atoms in the transition metal-rich phase ispreferably 50 at % to 70 at %. When the concentration of Fe atoms in thetransition metal-rich phase is in the above range, the effect of theinclusion of the transition metal-rich phase can be more effectivelyobtained. In contrast to what has been described above, when theconcentration of Fe atoms in the transition metal-rich phase is belowthe above range, there is a concern that the effect of the inclusion ofthe transition metal-rich phase in the grain boundary phase thatimproves the coercive force (Hcj) may become insufficient. In addition,when the concentration of Fe atoms in the transition metal-rich phase isbeyond the above range, there is a concern that the R₂T₁₇ phase or Femay be precipitated such that the magnetic properties are adverselyaffected.

In the invention, the volume ratio of the transition metal-rich phase inthe R-T-B-based magnet is investigated using a process described below.First, the R-T-B-based magent is embedded in a conductive resin, asurface in parallel with the orientation direction is cut, andmirror-polished. Next, the mirror-polished surface is observed using abackscattered electron image at a magnification of approximately 1500times, and the main phase, the R-rich phase and the transitionmetal-rich phase are determined using contrast. After that, the arearatio of the transition metal-rich phase per cross-section is computed,and, furthermore, the volume ratio is computed with an assumption thatthe transition metal-rich phase is spherical.

Since the R-T-B-based magnet of the embodiment is formed by molding andsintering an R-T-B-based alloy having a amount of B/TRE which satisfiesthe above Formula 1 and 0.1 at % to 2.4 at % of the metallic element M,the grain boundary phase includes the R-rich phase and the transitionmetal-rich phase, and the transition metal-rich phase has a lowerconcentration of the rare earth elements and a higher concentration ofFe atoms than the R-rich phase, the R-T-B-based magnet suppresses theamount of Dy, and has a large coercive force and magnetic propertiesexcellent enough to be a preferable material for motors.

Meanwhile, in the embodiment, it is also possible to make theR-T-B-based magnet have a higher concentration of Dy on the surface ofthe sintered magnet than in the magnet by attaching Dy metal or a Dycompound to the surface of the sintered R-T-B-based magnet, thermallytreating the magnet, and diffusing Dy in the sintered magnet, therebyfurther improving the coercive force.

The R-T-B-based magnet having a higher concentration of Dy on thesurface of the sintered magnet than in the magnet is specificallyproduced as follows. For example, the sintered R-T-B-based magnet isimmersed in a coating fluid obtained by mixing a solvent such as ethanoland dysprosium fluoride (DyF₃) at a predetermined ratio, therebyapplying the coating fluid to the R-T-B-based magnet. After that, adiffusion step in which a two-step thermal treatment is carried out onthe R-T-B-based magnet to which the coating fluid has been applied iscarried out. Specifically, a first thermal treatment in which theR-T-B-based magnet to which the coating fluid has been applied is heatedat a temperature of 900° C. for approximately one hour in an argonatmosphere, and the R-T-B-based magnet that has been subjected to thefirst thermal treatment is cooled to room temperature. After that, asecond thermal treatment in which the R-T-B-based magnet is again heatedat a temperature of 500° C. for approximately one hour in an argonatmosphere is carried out, and cooled to room temperature.

In addition to the above process, a process in which a metal is gasifiedand a film of the gaseous metal is attached to the surface of themagnet, a process in which an organic metal is decomposed so as toattach a film to the surface, and the like may be used as a process inwhich Dy metal or a Dy compound is attached to the surface of thesintered R-T-B-based magnet.

Meanwhile, instead of Dy metal or a Dy compound, Tb metal or a Tbcompound may be attached to the surface of the sintered R-T-B-basedmagnet and thermally treated. In this case, for example, when a coatingfluid containing a fluoride of Tb is applied to the surface of thesintered R-T-B-based magnet, and thermally treated, thereby diffusing Tbin the sintered magnet, it is possible to obtain an R-T-B-based magnethaving a higher concentration of Tb on the surface of the sinteredmagnet than in the magnet, and the coercive force can be furtherimproved.

In addition, it is also possible to further improve the coercive forceby depositing and thermally treating metal Dy or metal Tb on the surfaceof the R-T-B-based magnet and by diffusing Dy or Tb in the sinteredmagnet. In the R-T-B-based magnet of the embodiment, any of the abovetechniques can be used without any adverse effect.

The coercive force (Hcj) of the R-T-B-based magnet is preferably larger.In a case in which the R-T-B-based magent is used as a magnet in anelectromotive power steering motor of an automobile or the like, thecoercive force is preferably 20 kOe or more, and in a case in which theR-T-B-based magent is used as a magnet in a motor of an electricvehicle, the coercive force is preferably 30 kOe or more. When thecoercive force (Hcj) of the magnet in a motor of an electric vehicle isless than 30 kOe, there are cases in which the heat resistance becomesinsufficient for motors.

Second Embodiment

In the first embodiment, the R-T-B-based magnet was produced using theR-T-B-based alloy containing the metallic element; however, in a secondembodiment, unlike the first embodiment, the R-T-B-based magnet will beproduced using an alloy material for R-T-B-based rare earth sinteredmagnets containing a powder-form R-T-B-based alloy containing nometallic element and an additional metal (hereinafter, abbreviated to“R-T-B-based alloy material”).

When the R-T-B-based alloy material of the present embodiment is moldedand sintered in the same manner as in the first embodiment, theR-T-B-based magnet of the first embodiment can be obtained.

The R-T-B-based alloy material of the embodiment is an R-T-B-based alloymaterial including an R-T-B-based alloy containing R which is a rareearth element, T which is a transition metal essentially containing Fe,B and inevitable impurities, in which R accounts for 13 at % to 15 at %,B accounts for 4.5 at % to 6.2 at %, T accounts for balance, theproportion of Dy in all rare earth elements is in a range of 0 at % to65 at %, and the following Formula 1 is satisfied; and an additionalmetal made of a metallic elements M comprising one or more metalsselected from Al, Ga and Cu or an alloy containing the metallic elementM, in which the metallic element M is contained in a range of 0.1 at %to 2.4 at %,

0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1

in Formula 1, Dy represents a concentration (at %) of a Dy element, Brepresents a concentration (at %) of a boron element, and TRE representsa concentration (at %) of all the rare earth elements.

The R-T-B-based alloy material of the embodiment can be produced in thesame manner as the R-T-B-based alloy of the first embodiment using thesame R-T-B-based alloy as in the first embodiment except for the factthat the alloy does not contain the metallic element M. Therefore, theR-T-B-based alloy included in the R-T-B-based alloy material of theembodiment will not be described.

Similarly to the R-T-B-based alloy of the first embodiment, in theR-T-B-based alloy included in the R-T-B-based alloy material of theembodiment as well, the area ratio of the region including the R₂T₁₇phase is preferably 0.1% to 50%, and more preferably 0.1% to 25%. In acase in which the area ratio of the region including the R₂T₁₇ phase isin the above range, the generation of the transition metal-rich phase iseffectively accelerated, and an R-T-B-based magnet which sufficientlyincludes the transition metal-rich phase and has a large coercive forcecan be obtained. When the area ratio of the region including the R₂T₁₇phase is 50% or more, there are cases in which it is not possible tofully consume the R₂T₁₇ phase in a step of producing the R-T-B-basedmagnet, and there are cases in which the coercive force or squareness ofthe R-T-B-based magnet decreases.

Furthermore, in the R-T-B-based alloy included in the R-T-B-based alloymaterial of the embodiment as well, in a case in which the area ratio ofthe region including the R₂T₁₇ phase is in a range of 0.1% to 50%, sinceexcellent crushability can be obtained, the alloy is easily crushed, andit is possible to make the alloy into fine particles having a graindiameter of approximately 2 μm.

Meanwhile, the area ratio of the region including the R₂T₁₇ phase in theR-T-B-based alloy included in the R-T-B-based alloy material of theembodiment can be obtained in the same manner as in the R-T-B-basedalloy of the first embodiment.

The additional metal contained in the R-T-B-based alloy material of theembodiment is made of a metallic elements M comprising one or moremetals selected from Al, Ga and Cu or an alloy containing the metallicelement M.

The metallic element M is assumed to accelerate the generation of thetransition metal-rich phase during sintering and the thermal treatmentfor producing the R-T-B-based magnet.

The metallic element M is contained at 0.1 at % to 2.4 at % in theR-T-B-based alloy material. The amount of the metallic element M is morepreferably in a range of 0.7 at % to 1.4 at %. Since the R-T-B-basedalloy material of the embodiment contains 0.1 at % to 2.4 at % of themetallic element M, an R-T-B-based magnet including the R-rich phase andthe transition metal-rich phase can be obtained by sintering the alloymaterial.

One or more metals selected from Al Ga and Cu, which are contained inthe metallic element M accelerates the generation of the transitionmetal-rich phase during the sintering and thermal treatment of theR-T-B-based magnet without adversely affecting other magneticproperties, thereby effectively improving the coercive force (Hcj).

When the amount of the metallic element M is less than 0.1 at %, thereis a concern that the effect that accelerates the generation of thetransition metal-rich phase may be not sufficient such that thetransition metal-rich phase is not formed in the R-T-B-based magnet andit is not possible to sufficiently improve the coercive force (Hcj) ofthe R-T-B-based magnet. In addition, when the amount of the metallicelement M exceeds 2.4 at %, magnetic properties such as the remanence(Br) of the R-T-B-based magnet or the maximum energy product (BHmax)degrade.

In a case in which the R-T-B-based alloy material contains Cu, theconcentration of Cu is preferably 0.07 at % to 1 at %. In a case inwhich the concentration of Cu is less than 0.07 at %, the magnet becomesdifficult to sinter. In addition, in a case in which the concentrationof Cu exceeds 1 at %, the remanence (Br) of the R-T-B-based magnetdegrades, which is not preferable.

The R-T-B-based alloy material of the embodiment may further contain Siin addition to the R-T-B-based alloy and the additional metal. In a casein which the R-T-B-based alloy material contains Si, the amount of Si ispreferably in a range of 0.7 at % to 1.5 at %. When the amount of Si isin the above range, the coercive force further improves. The effect ofthe inclusion of Si weakens when the amount of Si is both less than 0.7at % and more than 1.5 at %.

“Process of Producing the R-T-B-Based Alloy Material”

The R-T-B-based alloy contained in the R-T-B-based alloy material of theinvention can be produced in the same manner as the R-T-B-based alloy ofthe first embodiment. In addition, when the powder of the obtainedR-T-B-based alloy and the powder of the additional metal are mixed, theR-T-B-based alloy material can be obtained.

“Process of Producing the R-T-B-Based Rare Earth Sintered Magnet”

The R-T-B-based magnet can be produced using the R-T-B-based alloymaterial of the embodiment, which is obtained in the above manner, inthe same manner as in a case in which the R-T-B-based alloy of the firstembodiment is used.

Meanwhile, generally, the grain size of the powder of the R-T-B-basedalloy is set in a range of 4 μm to 5 μm at d50 in order to improve thecoercive force of the R-T-B-based magnet; however, when the grain sizeis further decreased so as to decrease the sizes of the grains in theR-T-B-based magnet, it is possible to further improve the coerciveforce.

Meanwhile, even in the embodiment, similarly to the first embodiment, itis possible to further improve the coercive force by applying a fluorideof Dy or Tb to the surface of the R-T-B-based magnet, thermally treatingthe fluoride, and diffusing Dy or Tb in the sintered magnet. Inaddition, it is also possible to further improve the coercive force bydepositing Dy metal or Tb metal on the surface of the R-T-B-basedmagnet, thermally treating the magnet, and diffusing Dy or Tb in thesintered magnet.

In the process of producing the R-T-B-based magnet of the embodiment,since an alloy material in which the amount of B satisfies the aboveFormula 1 and the metallic element M is contained at 0.1 at % to 2.4 at% is used as the R-T-B-based alloy material, the R-T-B-based magnet ofthe invention which is made of a sintered body including a main phaseprimarily containing R₂Fe₁₄B and a grain boundary phase containing moreR than the main phase, in which the grain boundary phase includes theR-rich phase having a concentration of all atoms of the rare earthelements of 70 at % or more and the transition metal-rich phase having aconcentration of all the atoms of the rare earth elements in a range of25 at % to 35 at % can be obtained.

Furthermore, when the kind or use amount of the metallic element Mcontained in the R-T-B-based alloy of the embodiment, the volume ratioof the region including the R₂T₁₇ phase, and the composition of theR-T-B-based alloy are adjusted in the above ranges of the invention, andthe conditions such as the sintering temperature or the thermaltreatment after sintering are adjusted, it is possible to easily adjustthe volume ratio of the transition metal-rich phase in the R-T-B-basedmagnet to a preferable range of 0.005 vol % to 3 vol %. In addition, theR-T-B-based magnet which suppresses the amount of Dy and has apredetermined coercive force suitable for use can be obtained byadjusting the volume ratio of the transition metal-rich phase in theR-T-B-based magnet.

Since the R-T-B-based magnet of the embodiment is formed by molding andsintering an R-T-B-based alloy material having a amount of B/TRE whichsatisfies the above Formula 1 and having 0.2 at % to 5 at % of themetallic element M, the grain boundary phase includes the R-rich phaseand the transition metal-rich phase, and the transition metal-rich phasehas a lower concentration of all atoms of the rare earth elements thanthe R-rich phase and a higher concentration of Fe atoms than the R-richphase, the R-T-B-based magnet suppresses the amount of Dy, and has alarge coercive force and magnetic properties excellent enough to be apreferable material for motors.

Third Embodiment

In the second embodiment, the R-T-B-based alloy material containing thepowder-form R-T-B-based alloy containing no metallic element and theadditional metal has been described, however, in the present embodiment,an R-T-B-based alloy material containing an R-T-B-based alloy containinga metallic element and the additional metal will be described. That is,in the invention, the metallic element may be added to the R-T-B-basedalloy material in a step of casting the R-T-B-based alloy, in a stepbefore the sintering of the R-T-B-based alloy, or in both steps.

In a third embodiment, some of the metallic element contained in theR-T-B-based alloy material is added to the R-T-B-based alloy, and thepowder of the R-T-B-based alloy and the remnant of the metallic elementare mixed, thereby preparing an R-T-B-based alloy material, and anR-T-B-based magnet is produced using the R-T-B-based alloy material.

When the R-T-B-based alloy material of the embodiment is molded andsintered in the same manner as in the first and second embodiments, theR-T-B-based magnets of the first and second embodiments can be obtained.

The R-T-B-based alloy material of the embodiment is an R-T-B-based alloymaterial including an R-T-B-based alloy containing R which is a rareearth element, T which is a transition metal essentially containing Fe,a first metal comprising one or more metals selected from Al, Ga and Cu,B and inevitable impurities, in which R accounts for 13 at % to 15 at %,B accounts for 4.5 at % to 6.2 at %, T accounts for balance, theproportion of Dy in all rare earth elements is in a range of 0 at % to65 at %, and the following Formula 1 is satisfied; and an additionalmetal made of a second metal comprising one or more metals selected fromAl, Ga and Cu or an alloy containing the second metal, in which thefirst metal and the second metal are contained in a range of 0.1 at. %to 2.4 at. % in total,

0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1

in Formula 1, Dy represents a concentration (at %) of a Dy element, Brepresents a concentration (at %) of a boron element, and TRE representsa concentration (at %) of all the rare earth elements.

Both the first and second metals are one or more metals selected fromAl, Ga and Cu, and the same composition as the metallic element M in thefirst and second embodiment is formed using the sum of the first andsecond metals.

In addition, the amount of the sum of the first and second metals in theR-T-B-based alloy material is the same as those of the metallic elementM in the first and second embodiments.

The R-T-B-based alloy material of the embodiment is the same as theR-T-B-based alloy material of the second embodiment except for the factthat the R-T-B-based alloy contains the first metal, and the R-T-B-basedmagnet is the same as in the first and second embodiments. Therefore,the R-T-B-based material and the R-T-B-based magnet of the embodimentwill not be described.

Here, a process for generating the transition metal-rich phase includedin the R-T-B-based magnet of the invention will be described in detail.

In the invention, it is considered that the R₂T₁₇ phase included in theR-T-B-based alloy in the middle of being produced and/or the R-T-B-basedmagnet in the middle of being produced is used as a raw material for thetransition metal-rich phase in the R-T-B-based magnet in the thermaltreatment that is carried out once or plural times in a step ofproducing the R-T-B-based alloy and/or a step of producing theR-T-B-based magnet so as to generate the transition metal-rich phase.

The conditions of the thermal treatment that generates the transitionmetal-rich phase are determined depending on the kind or use amount ofthe metallic element M, which is used together with the R₂T₁₇ phase as araw material for the transition metal-rich phase, the generation amountof the R₂T₁₇ phase included in the R-T-B-based alloy and/or the sinteredR-T-B-based magnet, the composition of the R-T-B-based magnet, thegeneration amount of the necessary transition metal-rich phase, and thelike.

The thermal treatment that generates the transition metal-rich phase,specifically, can be carried out once or plural times on the R-T-B-basedalloy in the middle of being produced and/or the R-T-B-based magnet inthe middle of being produced at a temperature in a range of 400° C. to800° C., and more preferably in a range of 450° C. to 650° C., and thethermal treatment is preferably carried out in the step of producing theR-T-B-based alloy and/or the step of producing the R-T-B-based magnetfor a total of 0.5 hours to 5 hours, and more preferably for a total of1 hour to 3 hours.

When the temperature of the thermal treatment that generates thetransition metal-rich phase is lower than 400° C., there are cases inwhich the reaction among the rare earth element R, the 2-17 phase (R₂T₁₇phase) and the metallic element M during the thermal treatment becomesinsufficient and the transition metal-rich phase is not sufficientlygenerated. When the temperature of the thermal treatment that generatesthe transition metal-rich phase exceeds 800° C., there are cases inwhich atoms are rearranged in a way that the transition metal-rich phaseis not sufficiently generated.

In addition, when the total time of the thermal treatment that generatesthe transition metal-rich phase is less than 0.5 hours, there are casesin which the reaction among the rare earth element R, the 2-17 phase(R₂T₁₇ phase) and the metallic element M during the thermal treatmentbecomes insufficient and the transition metal-rich phase is notsufficiently generated. When the total time of the thermal treatmentthat generates the transition metal-rich phase exceeds 5 hours, thethermal treatment takes a long time so as to adversely affectproductivity, which is not preferable.

The thermal treatment that generates the transition metal-rich phase iscarried out once or plural times in the step of producing theR-T-B-based alloy and/or the step of producing the R-T-B-based magnet.The thermal treatment may be intended only for the generation of thetransition metal-rich phase or may be carried out using another thermaltreatment with a different intention such as sintering. The number oftimes of the thermal treatment necessary to generate the transitionmetal-rich phase is not particularly limited, but is preferably carriedout a plurality of times in order to sufficiently generate thetransition metal-rich phase.

Specifically, as the thermal treatment that generates the transitionmetal-rich phase, one or more treatments selected from the followingtreatments can be used: a treatment (temperature retention step) inwhich the cooling rate of the thin cast alloy pieces after casting,which is carried out when producing the R-T-B-based alloy, istemporarily slowed so as to accelerate the diffusion of components inthe alloy, a thermal treatment for generating the transition metal-richphase in the sintered R-T-B-based magnet, a thermal treatment fordiffusing Dy or Tb in the sintered R-T-B-based magnet, and the like.

Meanwhile, the thermal treatment that generates the transitionmetal-rich phase is preferably carried out at a temperature in a rangeof 400° C. to 800° C., but the optimal temperature in the above rangediffers depending on the state of the structure of the R-T-B-based alloyor the R-T-B-based magnet being thermally treated, for example, theoptimal temperature before sintering and the optimal temperature aftersintering are different, and therefore the optimal temperature isappropriately determined by the step in which the thermal treatment iscarried out among the step of casting the R-T-B-based alloy through thecompletion of the R-T-B-based magnet.

In addition, there is a tendency for the generation amount of thetransition metal-rich phase obtained through the thermal treatment thatgenerates the transition metal-rich phase to increase as the time of thethermal treatment that generates the transition metal-rich phaseincreases. However, in a case in which the temperature of theR-T-B-based alloy or the R-T-B-based magnet reaches the decompositiontemperature of the transition metal-rich phase or higher in steps afterthe thermal treatment that generates the transition metal-rich phase,there is a possibility that part or all of the generated transitionmetal-rich phase is decomposed and decreased.

In the thermal treatment that generates the transition metal-rich phase,it is assumed that the reactions represented by the following Formula 3and/or Formula 4 proceed.

In more detail, in a case in which the metallic element M that is usedas a raw material for the transition metal-rich phase in the thermaltreatment is solely present in the R-T-B-based alloy or the R-T-B-basedmagnet, which is a material being thermally treated, it is assumed thatthe reaction represented by the following Formula 3 proceeds in thethermal treatment that generates the transition metal-rich phase, andthe like.

R(rare earth element)+R₂T₁₇(R₂T₁₇ phase)+M(metallic element)→R₆T₁₃M(transition metal-rich phase)  Formula 3

Examples of the case in which the metallic element M is solely presentin a material being thermally treated include a thermal treatment forsintering which is carried out when producing the R-T-B-based magnetusing the R-T-B-based alloy material containing the R-T-B-based alloycontaining no metallic element and the additional metal, and the like.

In addition, in a case in which the metallic element M is contained inthe alloy grain boundary phase or the grain boundary phase in a materialbeing thermally treated, it is assumed that the reaction represented bythe following Formula 4 proceeds in the thermal treatment that generatesthe transition metal-rich phase.

RM(rare earth element containing the metallic element)+R₂T₁₇(R₂T₁₇phase)→R₆T₁₃M(transition metal-rich phase)  Formula 4

Examples of the case in which the metallic element M is contained in thealloy grain boundary phase or the grain boundary phase in a materialbeing thermally treated include a thermal treatment for sintering whichis carried out when producing the R-T-B-based magnet using theR-T-B-based alloy containing the metallic element, and the like.

In a case in which both a material solely containing the metallicelement M and a material containing the metallic element in the alloygrain boundary phase or the grain boundary phase are thermally treated,it is assumed that the reaction represented by the above Formula 3 andthe reaction represented by Formula 4 proceed at the same time in thethermal treatment that generates the transition metal-rich phase.Examples of the above case include a thermal treatment for sinteringwhich is carried out when producing the R-T-B-based magnet using theR-T-B-based alloy material containing the R-T-B-based alloy containingthe metallic element and the additional metal, and the like.

The size of the R₂T₁₇ phase in the R-T-B-based alloy is preferablysmaller. When the size of the R₂T₁₇ phase is large, it is not possibleto fully remove the R₂T₁₇ phase even when the reaction represented byFormula 3 or Formula 4 is caused, and there are cases in which the R₂T₁₇phase remains in the R-T-B-based magnet such that the coercive force orsquareness degrades. Specifically, the size of the R₂T₁₇ phase ispreferably 10 μm or less, and more preferably 3 μm or less. Meanwhile,the size of the R₂T₁₇ phase refers to the size of a single R₂T₁₇ phase,and is not the size of a region in which the R₂T₁₇ phase is present.

As such, in the invention, it is assumed that, when the thermaltreatment that generates the transition metal-rich phase is carried out,the transition metal-rich phase in the R-T-B-based magnet is generatedusing the R₂T₁₇ phase and the rare earth element R containing themetallic element M (or the metallic element M and the rare earth elementR) as raw materials as described in Formula 3 and/or Formula 4.

EXAMPLES Experiment Examples 1 to 17 and 41 to 46

Nd metal (purity: 99 wt % or more), Pr metal (purity: 99 wt % or more),Dy metal (purity 99 wt % or more), ferro-boron (Fe 80 wt %, B 20 wt %),iron ingot (purity: 99 wt % or more), Al metal (purity: 99 wt % ormore), Ga metal (purity: 99 wt % or more) and Cu metal (purity: 99 wt %or more) were weighed so as to obtain the alloy compositions of Alloys Ato L, N to Q and T to Z described in Table 1, furthermore, 2.3 at % ofCo metal (purity: 99 wt % or more) was weighed, and the components wereloaded in an alumina crucible.

Meanwhile, the amounts of Si described in the alloy compositionsdescribed in Table 1 refers to the amounts of Si that is notintentionally added to the alloy but is contained in the alloy as animpurity. In addition, Alloy N is an alloy manufactured with anintention of adding no metallic element M, Alloy O is an alloymanufactured with an intention of adding only Al as the metallic elementM, Alloy P is an alloy manufactured with an intention of adding only Gaas the metallic element M, and Alloy Q is an alloy manufactured with anintention of adding only Cu as the metallic element M. In addition, Alcontained in Alloys N, P and Q is an element that is not intentionallyadded but is incorporated from the alumina crucible.

After that, the inside of a high-frequency vacuum induction furnace intowhich the alumina crucible had been put was substituted with Ar, heatedto 1450° C. so as to melt the components, the molten alloy was pouredinto a copper roll with water cooling, and cast using a strip casting(SC) method at a roll rotating rate of 1.0 m/second so as to obtain anaverage thickness of approximately 0.3 mm, thereby obtaining thin castalloy pieces.

Next, the thin cast alloy pieces were cracked using a hydrogendecrepitation method described below. First, the thin cast alloy pieceswere coarsely cracked so as to obtain a diameter of approximately 5 mm,and put into a hydrogen atmosphere so as to absorb hydrogen.Subsequently, a thermal treatment in which the thin cast alloy piecesthat had been coarsely crushed so as to absorb hydrogen were heated to300° C. in a hydrogen atmosphere was carried out. After that, a thermaltreatment in which the pressure was reduced so as to desorb hydrogenand, furthermore, the thin cast alloy pieces were heated to 500° C. wascarried out so as to emit and remove the hydrogen in the thin cast alloypieces, and the thin cast alloy pieces were cooled to room temperature.

Next, zinc stearate (0.025 wt %) was added to the hydrogen-decrepitatedthin cast alloy pieces as a lubricant, and the hydrogen-decrepitatedthin cast alloy pieces were finely crushed to an average grain size(d50) of 4.5 μm using a jet mill (Hosokawa Micron 100AFG) andhigh-pressure nitrogen (0.6 MPa), thereby obtaining a powder-formR-T-B-based alloy.

The area ratios of the R₂T₁₇ phases in Alloys A to L, N to Q and T to Zobtained in the above manner were investigated using a method describedbelow.

A thin cast alloy piece having a thickness in a range of ±10% of theaverage thickness was embedded in a resin, a cross-section was cut inthe thickness direction, the cross-section was mirror-polished, and thengold or carbon for supplying conductivity was deposited, therebypreparing an observation specimen. A backscattered electron image of thespecimen was photographed at a magnification of 350 times using ascanning electron microscope (JSM-5310 manufactured by JEOL Ltd.).

FIG. 6 illustrates the backscattered electron image of Alloy F as anexample. In addition, the area ratios of the R₂T₁₇ phases in themeasured alloys among Alloys A to L, N to Q and T to Z are described inTable 4. In Table 4, symbol ‘-’ indicates that the area ratio of thecorresponding alloy is not measured.

Next, the powder-form R-T-B-based alloy obtained in the above manner waspress-molded using a machine for molding in a transverse magnetic fieldat a molding pressure of 0.8 t/cm², thereby preparing green compact.After that, the obtained green compact was sintered at a temperature ina range of 900° C. to 1200° C. in a vacuum. After that, the greencompact was thermally treated at two different temperatures of 800° C.and 500° C. and cooled, thereby manufacturing R-T-B-based magnets ofExperiment Examples 1 to 17 and Experiment Examples 41 to 46.

In addition, the magnetic properties of the respective R-T-B-basedmagnets obtained in Experiment Examples 1 to 17 and Experiment Examples41 to 46 were measured using a BH curve tracer (TPM 2-10 manufactured byToei Industry Co., Ltd.). The results are described in Table 4.

Experiment Examples 18 to 33

The powder-form R-T-B-based alloys obtained in Experiment Examples 1 to17 (Alloys A to H, J to L and N to Q) and powder-form Alloy R and Sipowder having an average grain size (d50) of 4.35 μm were prepared, thepowder-form alloy and Si powder were mixed so as to obtain thecomposition of a sintered magnet described in Table 2, thereby producingR-T-B-based alloy materials of Experiment Examples 18 to 33. Meanwhile,the grain size of the Si powder was measured using a laserdiffractometer.

Next, R-T-B-based magnets were manufactured in the same order as inExperiment Example 1 to 15 using the R-T-B-based alloy materialsobtained in the above manner.

In addition, the magnetic properties of the respective R-T-B-basedmagnets obtained in Experiment Examples 18 to 33 were measured in thesame manner as in Experiment Examples 1 to 17 using a BH curve tracer(TPM 2-10 manufactured by Toei Industry Co., Ltd.). The results aredescribed in Table 5.

Experiment Example 34

Nd metal (purity: 99 wt % or more), Pr metal (purity: 99 wt % or more),Dy metal (purity 99 wt % or more), ferro-boron (Fe 80 wt %, B 20 wt %),iron ingot (purity: 99 wt % or more), Si metal (purity: 99 wt % ormore), Al metal (purity: 99 wt % or more), Ga metal (purity: 99 wt % ormore) and Cu metal (purity: 99 wt % or more) were weighed so as toobtain the alloy compositions of Alloy S described in Table 3,furthermore, 2.3 at % of Co metal (purity: 99 wt % or more) was weighed,the components were loaded in an alumina crucible, a powder-formR-T-B-based alloy was obtained in the same order as in ExperimentExamples 1 to 17, and an R-T-B-based magnet was manufactured in the sameorder as in Experiment Examples 1 to 17 using the powder-formR-T-B-based alloy.

In addition, the magnetic properties of the respective R-T-B-basedmagnets obtained in Experiment Example 34 were measured in the samemanner as in Experiment Examples 1 to 17 using a BH curve tracer (TPM2-10 manufactured by Toei Industry Co., Ltd.). The results are describedin Table 6.

TABLE 1 Experiment Alloy composition (at %) Alloy Example R in total NdPr Dy B Fe Si Ga Al Cu M A 1 14.5 12.36 2.17 0.00 5.25 77.2 0.07 0.070.34 0.10 0.51 B 2 15.1 12.89 2.17 0.00 5.29 76.6 0.07 0.07 0.34 0.110.52 C 3 13.9 11.79 2.14 0.00 5.27 77.8 0.07 0.07 0.35 0.10 0.52 D 414.9 12.72 2.18 0.00 5.16 76.9 0.08 0.07 0.38 0.10 0.55 E 5 13.8 7.592.28 3.88 5.22 78.0 0.06 0.07 0.34 0.07 0.48 F 6 14.1 7.97 2.31 3.875.30 77.5 0.09 0.07 0.35 0.07 0.49 G 7 14.9 8.59 2.32 3.95 5.38 76.80.08 0.07 0.36 0.07 0.50 H 8 14.0 7.93 2.27 3.82 4.89 78.1 0.07 0.070.36 0.07 0.50 I 9 13.7 7.53 2.27 3.84 6.13 77.3 0.08 0.07 0.34 0.070.48 J 10 13.8 3.21 2.25 8.30 5.40 77.8 0.08 0.07 0.36 0.07 0.50 K 1114.4 3.73 2.25 8.38 5.45 77.1 0.06 0.07 0.34 0.07 0.48 L 12 13.3 2.732.25 8.25 5.34 78.4 0.07 0.07 0.33 0.07 0.47 T 13 14.9 8.72 2.56 3.616.17 77.3 0.07 0.00 0.47 0.10 0.57 N 14 14.6 8.31 2.29 3.97 5.46 79.60.10 0.00 0.08 0.00 0.08 O 15 14.6 8.31 2.28 3.95 5.45 79.5 0.09 0.000.39 0.00 0.39 P 16 14.6 8.31 2.28 3.95 5.43 79.6 0.09 0.07 0.07 0.000.14 Q 17 14.6 8.33 2.28 4.00 5.50 79.4 0.10 0.00 0.01 0.07 0.10 U 4114.4 10.69 3.68 0.00 5.18 79.6 0.09 0.24 0.51 0.00 0.75 V 42 14.4 10.703.67 0.00 5.18 79.3 0.09 0.49 0.51 0.00 1.00 W 43 14.4 10.79 3.65 0.005.29 77.3 0.07 1.95 0.48 0.00 2.43 X 44 14.8 11.05 3.78 0.00 5.34 78.00.08 0.54 0.49 0.05 1.08 Y 45 14.8 11.06 3.79 0.00 5.30 77.6 0.08 0.540.49 0.31 1.34 Z 46 14.4 10.69 3.70 0.00 5.06 76.0 0.09 0.14 0.47 0.110.72

TABLE 2 Experiment Sintered magnet composition (at %) Alloy Example R intotal Nd Pr Dy B Fe Si Ga Al Cu A 18 14.5 12.32 2.16 0.00 5.25 76.6 0.770.07 0.34 0.10 B 19 15.0 12.85 2.16 0.00 5.27 76.0 0.78 0.07 0.34 0.10 C20 13.9 11.75 2.13 0.00 5.25 77.2 0.76 0.07 0.35 0.10 D 21 14.8 12.632.16 0.00 5.12 76.3 0.78 0.07 0.37 0.10 E 22 13.7 7.54 2.26 3.86 5.1877.5 0.76 0.07 0.33 0.07 F 23 14.0 7.91 2.29 3.84 5.26 76.9 0.78 0.070.35 0.07 G 24 14.8 8.53 2.31 3.93 5.35 76.2 0.79 0.07 0.36 0.07 H 2513.9 7.87 2.26 3.80 4.86 77.6 0.78 0.07 0.36 0.07 J 26 13.7 3.18 2.238.24 5.36 76.5 1.50 0.07 0.36 0.07 K 27 14.3 3.71 2.23 8.32 5.41 75.91.50 0.07 0.34 0.07 L 28 13.2 2.71 2.23 8.19 5.30 77.2 1.48 0.07 0.330.07 R 29 14.0 7.90 2.25 3.84 5.24 73.2 4.71 0.00 0.33 0.10 N 30 14.68.31 2.29 3.97 5.46 79.6 0.81 0.00 0.08 0.00 O 31 14.6 8.31 2.28 3.955.45 79.5 0.80 0.00 0.39 0.00 P 32 14.6 8.31 2.28 3.95 5.43 79.6 0.800.07 0.07 0.00 Q 33 14.6 8.33 2.28 4.00 5.50 79.4 0.80 0.00 0.01 0.07

TABLE 3 Experiment Sintered magnet composition (at %) Alloy Example R intotal Nd Pr Dy B Fe Si Ga Al Cu S 34 14.1 7.94 2.25 3.92 5.19 77.1 0.740.00 0.34 0.12

TABLE 4 Area ratio Experi- of 2-17 Volume ratio ment phase- (BH) oftransition Al- Exam- containing Sq max Br Hcj metal-rich loy ple region(%) (%) (MGOe) (kG) (kOe) phase (%) A 1 0.00 94.8 46.5 13.9 11.1 — B 20.00 94.8 44.1 13.5 14.9 — C 3 0.10 95.0 48.2 14.2 10.4 1.49 D 4 0.0094.3 45.5 13.9 10.0 — E 5 — 94.3 33.7 11.7 33.9 — F 6 4.30 94.4 32.911.6 36.7 0.64 G 7 — 93.1 31.9 11.4 37.0 0.59 H 8 87.50 88.9 29.3 11.530.8 — I 9 0.10 93.5 32.0 11.5 28.9 — J 10 33.10 89.0 20.7 9.2 47.2 — K11 28.10 81.7 20.7 9.2 39.6 — L 12 87.50 82.5 20.8 9.3 42.9 1.67 T 13 —93.6 32.6 11.6 29.9 0.00 N 14 — 92.8 32.7 11.5 26.3 — O 15 — 93.6 31.011.2 31.1 — P 16 — 93.0 32.6 11.5 29.2 — Q 17 — 94.3 31.6 11.3 28.6 — U41 — 93.1 41.7 13.2 18.3 — V 42 — 93.5 42.7 13.3 18.0 — W 43 — 93.2 41.113.1 13.7 — X 44 — 94.9 42.1 13.2 19.6 — Y 45 — 90.5 43.9 13.5 18.6 — Z46 — 93.8 45.0 13.7 18.5 —

TABLE 5 Volume ratio of transition Experiment Sq (BH)max Br Hcjmetal-rich Alloy Example (%) (MGOe) (kG) (kOe) phase (%) A 18 94.0 43.713.5 13.3 — B 19 94.6 38.9 12.7 17.2 — C 20 93.8 44.2 13.6 13.1 2.63 D21 93.2 38.2 12.8 14.1 — E 22 93.4 33.1 11.6 37.4 — F 23 91.3 30.7 11.238.6 1.27 G 24 92.3 30.1 11.1 38.1 0.78 H 25 87.3 26.9 11.1 32.4 — J 2689.7 19.7 8.9 48.3 — K 27 77.1 18.8 8.8 45.0 — L 28 88.7 19.9 9.1 43.91.47 R 29 89.7 22.4 9.8 33.6 — N 30 94.3 30.7 11.2 29.0 — O 31 92.3 29.611.0 33.5 — P 32 90.9 30.8 11.2 30.8 — Q 33 94.3 30.0 11.0 40.3 —

TABLE 6 Area ratio Exper- of 2-17 Volume ratio iment phase- (BH) oftransition Al- Exam- containing Sq max Br Hcj metal-rich loy ple region(%) (%) (MGOe) (kG) (kOe) phase (%) S 34 — 92.9 31.4 11.3 35.8 0.19

In Tables 4 to 6, “Hcj” represents the coercive force, “Br” representsthe remanence, “Sq” represents the squareness, and “BHmax” representsthe maximum energy product. In addition, these magnetic properties arethe average of measured values of five R-T-B-based magnets.

In addition, the volume ratios of the transition metal-rich phases inthe R-T-B-based magnets of Experiment Examples 3 to 28 and 34 wereinvestigated using the method described below.

The R-T-B-based magnet was embedded in a conductive resin, a surface inparallel with the orientation direction was cut, and mirror-polished.The surface was observed using a backscattered electron image at amagnification of approximately 1500 times, and the main phase, theR-rich phase and the transition metal-rich phase were determined usingcontrast.

For examples, FIGS. 9 and 10( a) are the backscattered electron imagesof the R-T-B-based magnets obtained in Experiment Examples 6 and 23respectively. It is found from FIGS. 9 and 10( a) that white R-richphases and light gray transition metal-rich phases are present in thegrain boundaries of gray R₂T₁₄B phases.

The area ratio of the transition metal-rich phases per cross-section wascomputed using the backscattered electron image, and, furthermore, thevolume ratios of the respective experiment examples were computed withan assumption that the transition metal-rich phases are spherical.

The results are described in Tables 4 to 6. In Tables 4 to 6, symbol ‘-’indicates that the area ratio of the corresponding alloy is notmeasured.

In addition, it was confirmed that the R-T-B-based magnets of ExperimentExamples 18 to 34 were mainly made up of the main phase containingR₂Fe₁₄B, the R-rich phase and the transition metal-rich phase byinvestigating the compositions of the main phase and the grain boundaryphase using an electron probe micro analysis (FE-EPMA).

As described in Tables 1 and 4, in Experiment Examples 8 and 9 in whichB does not satisfy Formula 1, the amounts of Dy are substantially thesame, and the coercive forces (Hcj) are smaller than that in ExperimentExample 6 in which B satisfies Formula 1.

In Experiment Example 23 in which the addition amount of Si is in arange of 0.7 at % to 1.5 at %, the coercive force (Hcj) is larger thanthat in Experiment Example 29 in which the amount of the additionalmetal exceeds the upper limit of the invention.

In addition, FIG. 1 is a graph illustrating the relationships betweenB/TRE (B represents a concentration (at %) of a boron element, and TRErepresents a concentration (at %) of all the rare earth elements) andthe coercive force (Hcj) of Experiment Examples 1 to 4 and 18 to 21.While the R-T-B-based magnets of Experiment Examples 1 to 4 and 18 to 21do not contain Dy, the addition of Si which is the additional metal(Experiment Examples 18 to 21) increases the coercive force (Hcj) asillustrated in Experiment Examples 18 to 21.

At this time, the optimal width of B/TRE is estimated to beapproximately ±0.1 with respect to the peak.

In addition, FIG. 2 is a graph illustrating the relationships betweenB/TRE (B represents a concentration (at %) of a boron element, and TRErepresents a concentration (at %) of all the rare earth elements) andthe coercive force (Hcj) of Experiment Examples 5 to 9 and 22 to 25. TheR-T-B-based magnets of Experiment Examples 5 to 9 and 22 to 25 containapproximately 3.8 at % of Dy. The coercive forces are different due tothe different amounts of B/TRE, and the coercive forces are at themaximum when B/TRE is 0.37. In addition, it is found that the additionof Si which is the additional metal (Experiment Examples 22 to 25)increases the coercive force as illustrated in Experiment Examples 22 to25. At this time, the optimal width of B/TRE is estimated to beapproximately ±0.1 with respect to the peak.

In addition, FIG. 3 is a graph illustrating the relationships betweenB/TRE (B represents a concentration (at %) of a boron element, and TRErepresents a concentration (at %) of all the rare earth elements) andthe coercive force (Hcj) of Experiment Examples 10 to 12 and 26 to 28.The R-T-B-based magnets of Experiment Examples 10 to 12 and 26 to 28contain approximately 8.3 at % of Dy. The coercive forces are differentdue to the different amounts of B/TRE, and the coercive forces are atthe maximum when B/TRE is 0.39.

In addition, it is found that the addition of Si which is the additionalmetal (Experiment Examples 24 to 26) increases the coercive force. Atthis time, the optimal width of B/TRE is estimated to be approximately±0.1 with respect to the peak.

Experiment Example 14 is an alloy manufactured without adding Cu, Al, Gaand Si, and has a significantly smaller coercive force than ExperimentExample 6 which has a most similar composition to Experiment Example 14.In Experiment Example 15 manufactured by adding only Al to thecomponents of Experiment 14, Experiment Example 16 manufactured byadding only Ga to the components of Experiment 14 and Experiment Example17 manufactured by adding only Cu to the components of Experiment 14,the coercive forces are larger than in Experiment Example 14. Thisindicates that any one of Al, Ga and Cu is essential in order toincrease the coercive force.

Furthermore, in Experiment Examples 30 to 33 manufactured by adding Sito Alloys N to Q, the coercive forces are increased, which indicatesthat the addition of two or more metals M is preferable. Particularly,in Experiment Example 33 manufactured by adding Si powder to Alloy Q, asignificant improvement of the coercive force is observed. In addition,in Experiment Example 33, the coercive force becomes 2 kOe or largerthan that in Experiment Example 24 having a similar composition, whichindicates that the addition of Cu and Si is particularly preferable.

When Experiment Examples 14 to 17 having substantially the sameconcentrations of Dy are compared, while the coercive force is small inExperiment Example 14 in which the concentration of the metallic elementM is 0.08 at %, the coercive forces are large in Experiment Examples 15to 17 in which the concentrations of the metallic element M is 0.1 at %or more.

In addition, when Experiment Examples 41 to 46 containing no Dy arecompared, in Experiment Example 43 (the concentration of the metallicelement M is 2.43 at %), the coercive force is smaller than those inExperiment Example 41 (the concentration of the metallic element M is0.75 at %) and Experiment Example 42 (the concentration of the metallicelement M is 1.00 at %).

Based on what has been described above, it is indicated that the amountof the metallic element M is preferably in a range of 0.1 at % to 2.4 at%.

Among Experiment Examples 1 to 4 and 41 to 46 containing no Dy, thecoercive forces are large in Experiment Examples 41, 42 and 44 to 46(the concentration of the metallic element M is in a range of 0.72 at %to 1.34 at %). Based on what has been described above, it is indicatedthat the amount of the metallic element M is preferably in a range of0.7 at % to 1.4 at %.

Experiment Example 34 described in Tables 3 and 6 is an alloymanufactured by adding all metallic elements in the step of alloycasting. When Experiment Example 34 is compared with Experiment Example5 in Tables 1 and 4, which have substantially the same amounts of Dy, itis found that Experiment Example 34 exhibits a larger coercive forcethan Experiment Example 5.

From the results of Tables 1 to 6, it is found that, both in a case inwhich the metallic elements are alloy-cast and a case in which an alloyand the additional metal are mixed, the effect that improves thecoercive force of the magnet can be obtained.

FIGS. 8 to 10( a) are microscope photographs of the R-T-B-based magnets.FIG. 8 is a backscattered electron image of Experiment Example 9, FIG. 9is a backscattered electron image of Experiment Example 6, and FIG. 10(a) is a backscattered electron image of Experiment Example 23. Inaddition, FIG. 10( b) is a schematic view for describing the microscopephotograph of the R-T-B-based magnet illustrated in FIG. 10( a). In thebackscattered electron images illustrated in FIGS. 8 to 10( a) and theschematic view illustrated in FIG. 10( b), the gray portions are theR₂T₁₄B phase, the white portions are the R-rich phase, and the lightgray portions are the transition metal-rich phase.

As described in Tables 1 and 2, the R-T-B-based magnets of ExperimentExamples 6, 9 and 23 have substantially the same amounts of Dy. B/TRE ofExperiment Example 9 is beyond the range of the invention. On the otherhand, B/TRE of Experiment Example 6 is a value in the range of theinvention, and Experiment Example 23 is an alloy manufactured by addingSi to Experiment Example 6. In FIG. 8, the transition metal-rich phasegenerated is rarely observed. It is found that, in FIG. 9, only a smallamount of the transition metal-rich phase generated is observed and, inFIG. 10( a), a larger amount of the transition metal-rich phase isgenerated. From FIGS. 8 to 10( a), it is found that, when B/TRE isappropriately selected and, furthermore, the additional metal isappropriately added, it is possible to increase the generation of thetransition metal-rich phase.

In FIG. 8, several crushed particles are molten so as to form the mainphase. In FIG. 9, crushed particles are not mixed and individually formthe main phases. In FIG. 10( a), a shape in which the main phases formedof the respective crushed particles are surrounded by the grain boundaryphases can be clearly observed.

Experiment Example 35

Nd metal (purity: 99 wt % or more), Pr metal (purity: 99 wt % or more),Dy metal (purity 99 wt % or more), Al metal (purity: 99 wt % or more),ferro-boron (Fe 80 wt %, B 20 wt %), iron ingot (purity: 99 wt % ormore), Ga metal (purity: 99 wt % or more), Cu metal (purity: 99 wt % ormore) and Co metal (purity: 99 wt % or more) were weighed so as toobtain the alloy compositions of Alloy S described in Table 7, andloaded in an alumina crucible.

TABLE 7 Nd Pr Dy Al Fe Ga Cu Co B 10.0 3.4 0.6 0.5 bal. 0.1 0.1 0.6 5.2

After that, thin cast alloy pieces were produced (casting step) usingthe production apparatus 1 of an alloy illustrated in FIG. 11. First,the inside of a high-frequency vacuum induction furnace (meltingapparatus) into which the alumina crucible had been put was substitutedwith Ar, and heated to 1450° C., thereby preparing molten alloy. Next,the obtained molten alloy was supplied to a rotating copper roll withwater cooling at a roll rotating rate of 1.0 m/second and solidified,thereby preparing a cast alloy. After that, the cast alloy was detachedfrom the cooling roll 22, and made to pass between crushing rolls in thecrushing apparatus 21 so as to be crushed, thereby obtaining thin castalloy pieces having an average thickness of 0.3 mm. Meanwhile, thecasting step was carried out in an argon atmosphere.

The crushed thin cast alloy pieces were made to pass through the hopper7, stacked on the openable stages 33 in a “close” state, heated usingthe heater 31, a temperature retention step in which the 800° C.-hotcast alloy was maintained at a certain temperature for 60 seconds wascarried out, and the openable stages 33 were set into a “open” state,thereby finishing the temperature retention step.

The thin cast alloy piece of Experiment Example 35 obtained in the abovemanner was embedded in a resin, a mirror-polished cross-section wasobserved using a backscattered electron image at a magnification of 350times, the main phase and the alloy grain boundary phase were determinedusing contrast, and the distances between adjacent alloy grain boundaryphases were investigated in the following manner. That is, straightlines were drawn at intervals of 10 μm in parallel with the cast surfaceon the respective images of the 350 times-magnified backscattered imagesof the thin cast alloy pieces of Experiment Example 35, the intervalsbetween the alloy grain boundary phases traversing the straight lineswere respectively measured, and the average value thereof was computed.As the distance between adjacent alloy grain boundary phases decreases,crushability becomes superior.

In addition, a plurality of thin cast alloy pieces that were the same asthe thin cast alloy pieces of Experiment Example 35 except for the factthat the concentrations of the B element and the Fe element in the alloycompositions described in Table 7 were changed were prepared, and thedistances between adjacent alloy grain boundary phases were investigatedin the same manner as those of the thin cast alloy pieces of ExperimentExample 35. The results are illustrated in FIGS. 12( a) to 12(c), 13(a)and 13(b).

FIG. 12( a) is a graph illustrating the relationship between thedistance between the alloy grain boundary phases and the concentrationof B in the thin cast alloy pieces, FIG. 12( b) is a graph illustratingthe relationship between the distance between the alloy grain boundaryphases and B/TRE (B represents the concentration (at %) of the boronelement and TRE represents the concentration (at %) of all rare earthelements) in the thin cast alloy pieces, and FIG. 12( c) is a graphillustrating the relationship between the distance between the alloygrain boundary phases and Fe/B (the ratio of the amount of Fe to theamount of B (B represents the concentration (at %) of the boron elementand Fe represents the concentration (at %) of the iron element)) in thethin cast alloy pieces.

From FIG. 12( a), it is found that, in a case in which the amount of Bis in a range of 5.0 at % to 6.0 at %, the distances between the alloygrain boundary phases are short, and the grains become fine. Inaddition, it is found that, when the amount of B becomes smaller than5.0 at %, the intervals between the alloy grain boundary phases abruptlywiden.

From FIG. 12( b), it is found that, in a case in which B/TRE is in arange of 0.355 to 0.38, the distances between the alloy grain boundaryphases are short, and the grains become fine. In addition, it is foundthat, when B/TRE becomes less than 0.355, the intervals between thealloy grain boundary phases abruptly widen.

FIG. 13( a) is a microscope photograph of a cross-section of a thin castalloy piece for which Fe/B is 15.5, and FIG. 13( b) is a microscopephotograph of a cross-section of a thin cast alloy piece for which Fe/Bis 16.4. In the backscattered electron images illustrated in FIGS. 13(a) and 13(b), gray portions are the main phase and the white portionsare the alloy grain boundary phase. It is found that, in the thin castalloy piece illustrated in FIG. 13( a), the alloy grain boundary phasesform a fine net-like shape. In contrast to this, in the thin cast alloypiece illustrated in FIG. 13( b), needle-like alloy grain boundaryphases and island-like main phases are observed.

From FIG. 12( c), it is found that, as Fe/B increases from 13, theintervals between the alloy grain boundary phases become narrow, and thedistance between the alloy grain boundary phases become particularlyshort at Fe/B in a range of 15 to 16. In addition, from FIGS. 12( c),13(a) and 13(b), it is found that, in a case in which Fe/B is in a rangeof 13 to 16, the distances between the alloy grain boundary phasesbecome short and the grains become fine compared with a case in whichFe/B exceeds 16. In addition, from FIG. 12( c), it is found that, whenFe/B exceeds 16, the intervals between the alloy grain boundary phasesbecome abruptly wide.

Experiment Example 36

Thin cast alloy pieces were produced (casting step) in the same manneras in Experiment Example 35 except for the fact that the components wereweighed to obtain the alloy composition described in table 7, loaded inan alumina crucible, and the atmosphere during the casting step was setto the following atmosphere using the production apparatus 1 of an alloyillustrated in FIG. 11.

That is, the casting step was carried out while supplying helium to anargon atmosphere, the cast alloy was cooled using the cooling roll 22 inan atmosphere containing helium, and, after the temperature retentionstep, the thin cast alloy pieces accommodated in the storage container 4were cooled in the atmosphere containing helium.

For the thin cast alloy pieces of Experiment Example 36 obtained in theabove manner, the distances between adjacent alloy grain boundary phaseswere investigated in the same manner as in Experiment Example 35. Theresults of the investigation of the distances between adjacent alloygrain boundaries of Experiment Examples 35 and 36 are illustrated inFIG. 14. In FIG. 14, black Δ indicates the results of Experiment Example35, and  indicates the results of Experiment Example 36.

The graph illustrated in FIG. 14 illustrates the results obtained bypreparing five thin cast alloy pieces of both Experiment Examples 35 andExperiment Examples 36, measuring the intervals between the alloy grainboundary phases in the same manner as described above, classifying themeasured values of the respective intervals between the alloy grainboundary phases every 0.2 μm, and computing the ratios of the number ofthe measured values appearing in the respective ranges to the number ofall the measured values of the intervals between the alloy grainboundary phases ((the number of the measured values appearing in eachrange/the number of all the measured values)×100(%)).

As illustrated in FIG. 14, in Experiment Example 36 which is the thincast alloy pieces for which the casting step is carried out in anatmosphere containing helium, the intervals between the alloy grainboundaries become narrow compared with Experiment Example 35 which isthe thin cast alloy pieces on which the casting step is carried out inan argon atmosphere. Based on what has been described above, it is foundthat, when the casting step is carried out in an atmosphere containinghelium, the grain diameters in the alloy structure become small, andexcellent crushability can be obtained.

Experiment Example 37

Thin cast alloy pieces were produced (casting step) in the same manneras in Experiment Example 35 except for the fact that the components wereweighed to obtain the alloy composition of Alloy F described in Table 1,loaded in an alumina crucible, and the history of the coolingtemperature while the temperature of the produced cast alloy reached 50°C. from 1200° C. was set to the (a) condition illustrated in FIGS. 15(a) to 15(c) and Table 8 using the production apparatus 1 of an alloyillustrated in FIG. 11.

TABLE 8 a) condition b) condition Elapsed Cooling Elapsed CoolingTemperature Time time rate Temperature Time time rate (° C.) (seconds)(seconds) (° C./second) (° C.) (seconds) (seconds) (° C./second) 1200 01200 0.0 900 0.3 0.3 1000 900 0.3 0.3 1000 700 0.5 0.8 400 800 0.25 0.6400 600 50 50.8 2 800 0 60.6 0 50 550 600.8 1 600 100 160.6 2 50 550710.6 1

Next, the thin cast alloy pieces were cracked using the hydrogendecrepitation method in the same manner as in Experiment Example 1,thereby obtaining a powder-form R-T-B-based alloy of Experiment Example37.

Meanwhile, the average grain size (d50) of the powder-form R-T-B-basedalloy was 4.5 μm.

The powder-form R-T-B-based alloy of Experiment Example 37 obtained inthe above manner was press-molded using a machine for molding in atransverse magnetic field at a molding pressure of 0.8 t/cm², therebypreparing green compact. After that, the obtained green compact wassintered at a temperature in a range of 900° C. to 1200° C. in a vacuum.After that, the green compact was thermally treated at two differenttemperatures of 800° C. and 500° C. and cooled, thereby manufacturing aplurality of R-T-B-based magnets of Experiment Example 37.

The magnetic properties of the plurality of the obtained R-T-B-basedmagnets of Experiment Example 37 were measured respectively using a BHcurve tracer (TPM 2-10 manufactured by Toei Industry Co., Ltd.). Theresults are illustrated in FIGS. 16( a) to 16(c).

Experiment Example 38

Thin cast alloy pieces were produced in the same manner as in ExperimentExample 37 except for the fact that the history of the coolingtemperature while the temperature of the produced cast alloy reached 50°C. from 1200° C. was set to the (b) condition illustrated in FIGS. 15(a) to 15(c) and Table 8, and a powder-form R-T-B-based alloy ofExperiment Example 38 was obtained in the same manner as in ExperimentExample 37 using the thin cast alloy pieces.

Meanwhile, the average grain size (d50) of the powder-form R-T-B-basedalloy was 4.5 μm.

A plurality of R-T-B-based magnets of Experiment Example 38 weremanufactured in the same manner as in Experiment Example 37 using thepowder-form R-T-B-based alloy of Experiment Example 38 obtained in theabove manner, and the magnetic properties of the plurality of theobtained R-T-B-based magnets of Experiment Example 38 were measuredrespectively using a BH curve tracer (TPM 2-10 manufactured by ToeiIndustry Co., Ltd.). The results are illustrated in FIGS. 16( a) to16(c).

Experiment Example 39

Powder made of the R-T-B-based alloy obtained in Experiment Example 37and Si powder having an average grain size (d50) of 4.35 μm wereprepared, and mixed so as to obtain the composition of ExperimentExample 23 described in Table 2, thereby producing an R-T-B-based alloymaterial of Experiment Example 39. Meanwhile, the grain size of the Sipowder was measured using a laser diffractometer.

Experiment Example 40

Powder made of the R-T-B-based alloy obtained in Experiment Example 38and Si powder having an average grain size (d50) of 4.35 μm wereprepared, and mixed so as to obtain the composition of ExperimentExample 23 described in Table 2, thereby producing an R-T-B-based alloymaterial of Experiment Example 40. Meanwhile, the grain size of the Sipowder was measured using a laser diffractometer.

Next, a plurality of R-T-B-based magnets of Experiment Example 39 and aplurality of R-T-B-based magnets of Experiment Example 40 weremanufactured respectively in the same manner as in Experiment Example 37using the R-T-B-based alloy materials of Experiment Examples 39 and 40obtained in the above manner.

In addition, the magnetic properties of a plurality of the obtainedR-T-B-based magnets of Experiment Examples 39 and 40 were measured usinga BH curve tracer (TPM 2-10 manufactured by Toei Industry Co., Ltd.) inthe same manner as in Experiment Example 37. The results are illustratedin FIGS. 16( a) to 16(c).

FIG. 16( a) is a graph illustrating the coercive forces (Hcj) of theR-T-B-based magnets of Experiment Examples 37 to 40, FIG. 16( b) is agraph illustrating the remanence (Br) of the R-T-B-based magnets ofExperiment Examples 37 to 40, and FIG. 16( c) is a graph illustratingthe relationship between the remanence (Br) and coercive forces (Hcj) ofthe R-T-B-based magnets of Experiment Examples 37 to 40. Meanwhile, thedotted line illustrated in FIG. 16( c) represents an equivalent line. Inaddition, in FIG. 16, Δ indicates the results of Experiment Example 37,o indicates the results of Experiment Example 38, black Δ indicates theresults of Experiment Example 39, and  indicates the results ofExperiment Example 40.

As illustrated in FIG. 16( a), the coercive forces (Hcj) were larger inExperiment Examples 38 and 40 in which the temperature retention step ofmaintaining the 800° C.-hot cast alloy at a certain temperature for 60seconds was carried out than in Experiment Examples 37 and 39 in whichthe temperature retention step was not carried out. In addition, thecoercive force (Hcj) was larger in the R-T-B-based magnet of ExperimentExample 40 for which the Si-added R-T-B-based alloy material was usedthan in the R-T-B-based magnet of Experiment Example 38 for which theR-T-B-based alloy material to which no Si had been added was used.

As illustrated in FIG. 16( b), the remanence (Br) differences were smallwhen Experiment Examples 38 and 40 in which the temperature retentionstep was carried out and Experiment Example 37 ad 39 in which thetemperature retention step was not carried out were compared and whenthe R-T-B-based magnets of Experiment Examples 39 and 40 in which theSi-added R-T-B-based alloy material was used and the R-T-B-based magnetsof Experiment Example 37 and 38 in which the R-T-B-based alloy materialto which no Si had been added was used were compared.

As illustrated in FIG. 16( c), it is found that Experiment Examples 38and 40 in which the temperature retention step was carried out arelocated on the right side of the equivalent line, and have a largercoercive force than cases in which the temperature retention step wasnot carried out.

Experiment Example 47

The powder-form R-T-B-based alloy produced to obtain the composition ofthe sintered magnet of Experiment Example 47 described in Table 9 waspress-molded using a machine for molding in a transverse magnetic fieldat a molding pressure of 0.8 t/cm², thereby preparing green compact.After that, the obtained green compact was sintered at a temperature ina range of 900° C. to 1200° C. in a vacuum. After that, the greencompact was thermally treated at two different temperatures of 800° C.and 500° C. and cooled, thereby manufacturing an R-T-B-based magnets ofExperiment Example 47.

TABLE 9 Magnet composition (at %) Experiment R in Example total Nd Pr DyB Fe Si Ga Al Cu M 47 14.8 11.05 3.79 0.00 5.62 77.8 0.08 0.54 0.49 0.211.2 48 14.9 11.05 3.79 0.10 5.62 77.8 0.08 0.54 0.49 0.21 1.2 49 14.113.96 0.14 0.00 5.77 80.2 0.00 0.23 0.20 0.09 0.5 50 14.1 13.96 0.140.03 5.77 80.2 0.00 0.23 0.20 0.09 0.5

Experiment Example 48

A coating fluid containing Dy was applied to a surface of the thermallytreated R-T-B-based magnet produced in the same manner as in ExperimentExample 47. As the coating fluid containing Dy, a mixture obtained bymixing ethanol and dysprosium fluoride (DyF₃) at a weight ratio of 1:1was used. In addition, the coating fluid was applied to the surface ofthe R-T-B-based magnet by immersing the sintered R-T-B-based magnet in acontainer for 1 minute while ultrasonic-dispersing the coating fluid inthe container.

Subsequently, the first thermal treatment in which the R-T-B-basedmagnet to which the coating fluid had been applied was heated at atemperature of 900° C. for one hour in an argon atmosphere to whichargon was supplied at a flow rate of 100 ml/min was carried out, and theR-T-B-based magnet was cooled to room temperature. After that, thesecond thermal treatment in which the R-T-B-based magnet was heated at atemperature of 500° C. for one hour in the same atmosphere as in thefirst thermal treatment was carried out, and the R-T-B-based magnet wascooled to room temperature (diffusion step), thereby obtaining anR-T-B-based magnet of Experiment Example 48.

Experiment Example 49

An R-T-B-based magnet of Experiment Example 49 was obtained in the samemanner as in Experiment Example 47 except for the fact that apowder-form R-T-B-based alloy produced to obtain the composition of thesintered magnet of Experiment Example 49 described in Table 9 was used.

Experiment Example 50

A diffusion step in which a coating fluid containing Dy was applied to asurface of a thermally treated R-T-B-based magnet produced in the samemanner as in Experiment Example 49 in the same manner as in ExperimentExample 48 was carried out, thereby obtaining an R-T-B-based magnet ofExperiment Example 50.

Regarding the compositions of the R-T-B-based magnets of ExperimentExamples 47 to 50 obtained in the above manner, the rare earth elements,iron, copper, cobalt, aluminum, gallium and boron were measured usingfluorescent X-ray analysis (XRF); carbon, nitrogen and oxygen weremeasured using a gas analysis apparatus; and other impurity elementscontained in a small amount were measured using induced coupling plasmaemission spectrometry (ICP). The results are described in Table 9.

When Experiment Examples 47 and 48 described in Table 9 are compared,when the diffusion step in which a thermal treatment is carried out byapplying the coating fluid containing Dy is completed, the concentrationof Dy contained in the R-T-B-based magnet increases. In addition, whenExperiment Examples 49 and 50 described in Table 9 are compared, whenthe diffusion step is carried out, the concentration of Dy contained inthe R-T-B-based magnet increases.

In addition, the magnet compositions of Experiment Examples 47 and 48described in Table 9 are in the range of the invention, and the magnetcompositions of Experiment Examples 49 and 50 have a value of “B/TRE”outside the range of the invention.

In addition, the R-T-B-based magnets of Experiment Examples 47 and 48were embedded in a conductive resin respectively, a surface in parallelwith the orientation direction was cut, and mirror-polished. The surfacewas observed using a backscattered electron image at a magnification ofapproximately 1500 times, and the main phase, the R-rich phase and thetransition metal-rich phase were determined using contrast.

Furthermore, for the R-T-B-based magnets of Experiment Examples 47 and48, the compositions of the main phase and the grain boundary phase (theR-rich phase and the transition metal-rich phase) were confirmed usingan electron probe micro analyzer (FE-EPMA) respectively.

As a result, the R-T-B-based magnets of Experiment Examples 47 and 48which are the examples of the invention included the main phase, theR-rich phase and the transition metal-rich phase.

In addition, the magnetic properties of the R-T-B-based magnets ofExperiment Examples 47 to 50 were measured respectively using a BH curvetracer (TPM 2-10 manufactured by Toei Industry Co., Ltd.). The resultsare illustrated in FIGS. 17( a) and 17(b) and Tables 10 and 11.

TABLE 10 Experiment Experiment Example 47 Example 48 Difference Br (kG)13.67 13.52 −0.15 Hcj (kOe) 17.47 22.41 4.95

TABLE 11 Experiment Experiment Example 49 Example 50 Difference Br (kG)14.84 14.72 −0.13 Hcj (kOe) 11.72 14.04 2.32

In Tables 10 and 11, “Hcj” represents the coercive force, and “Br”represents the remanence. In addition, these magnetic properties are theaverage of measured values of five R-T-B-based magnets respectively.

FIG. 17( a) is a graph illustrating the second quadrants of thehysteresis curves of Experiment Examples 47 and 48, and FIG. 17( b) is agraph illustrating the second quadrants of the hysteresis curves ofExperiment Examples 49 and 50. Here, the vertical axis indicatesmagnetization J, and the horizontal axis indicates magnetic fields H.The hysteresis curves illustrated in FIGS. 17( a) and 17(b) weremeasured using a BH curve tracer (TPM 2-10 manufactured by Toei IndustryCo., Ltd.). In FIGS. 17( a) and 17(b), the points at which the curvesintersect the horizontal axes indicate the values of the coercive force(Hcj), and the points at which the curves intersect the vertical axesindicate the values of the remanence “Br”.

As illustrated in FIG. 17( a) and Table 10, the coercive force issignificantly improved in Experiment Example 48 in which the diffusionstep was carried out compared with Experiment Example 47. In addition,when Experiment Examples 47 and 48 are compared, the remanence slightlychanges.

As illustrated in FIG. 17( b) and Table 11, the coercive force isimproved in Experiment Example 50 in which the diffusion step wascarried out compared with Experiment Example 49, but the change issmaller than the difference between Experiment Examples 47 and 48illustrated in FIG. 17( a) and Table 10, and the effect that improvesthe coercive force being small. In addition, when Experiment Examples 50and 49 are compared, the remanence slightly changes.

INDUSTRIAL APPLICABILITY

The invention can be applied to an alloy for R-T-B-based rare earthsintered magnets and an alloy material for R-T-B-based rare earthsintered magnets which have excellent magnetic properties and from whichR-T-B-based rare earth sintered magnets that are a preferable materialfor motors can be obtained.

REFERENCE SIGNS LIST

-   -   1 PRODUCTION APPARATUS    -   2 CASTING APPARATUS    -   3 HEATING APPARATUS    -   4 STORAGE CONTAINER    -   5 CONTAINER    -   6 CHAMBER    -   6 a CASTING CHAMBER    -   6 b HEAT RETENTION AND STORAGE CHAMBER    -   7 HOPPER    -   21 CRUSHING APPARATUS    -   31 HEATING HEATER    -   32 OPENABLE STAGE GROUP    -   33 OPENABLE STAGE

1. An alloy for R-T-B-based rare earth sintered magnets, the alloycomprising: R which is a rare earth element; T which is a transitionmetal essentially comprising Fe; a metallic element M comprising one ormore metals selected from Al, Ga and Cu; B; and inevitable impurities,wherein R accounts for 13 at % to 15 at %, B accounts for 4.5 at % to6.2 at %, M accounts for 0.1 at % to 2.4 at %, T accounts for balance, aproportion of Dy in all rare earth elements is in a range of 0 at % to65 at %, and the following Formula 1 is satisfied0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1 wherein, Dy represents aconcentration (at %) of a Dy element, B represents a concentration (at%) of a boron element, and TRE represents a concentration (at %) of allthe rare earth elements.
 2. The alloy for R-T-B-based rare earthsintered magnets according to claim 1, wherein M accounts for 0.7 at %to 1.4 at %.
 3. The alloy for R-T-B-based rare earth sintered magnetsaccording to claim 1, further comprising Si.
 4. The alloy forR-T-B-based rare earth sintered magnets according to claim 1, wherein anarea ratio of a region including an R₂T₁₇ phase is in a range of 0.1% to50%.
 5. An alloy material for R-T-B-based rare earth sintered magnets,the alloy material comprising: an R-T-B-based alloy comprising R whichis a rare earth element; T which is a transition metal essentiallycomprising Fe; B and inevitable impurities, in which R accounts for 13at % to 15 at %, B accounts for 4.5 at % to 6.2 at %, T accounts forbalance, a proportion of Dy in all rare earth elements is in a range of0 at % to 65 at %, and the following Formula 1 is satisfied; and anadditional metal made of a metallic elements M comprising one or moremetals selected from Al, Ga and Cu or an alloy comprising the metallicelement M, wherein the alloy material for R-T-B-based rare earthsintered magnets comprises the metallic element M in a range of 0.1 at %to 2.4 at %,0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1 in Formula 1, Dy representsa concentration (at %) of a Dy element, B represents a concentration (at%) of a boron element, and TRE represents a concentration (at %) of allthe rare earth elements.
 6. An alloy material for R-T-B-based rare earthsintered magnets, the alloy material comprising: an R-T-B-based alloycomprising R which is a rare earth element; T which is a transitionmetal essentially comprising Fe; a first metal comprising one or moremetals selected from Al, Ga and Cu; B and inevitable impurities, inwhich R accounts for 13 at % to 15 at %, B accounts for 4.5 at % to 6.2at %, T accounts for balance, a proportion of Dy in all rare earthelements is in a range of 0 at % to 65 at %, and the following Formula 1is satisfied; and an additional metal made of a second metal comprisingone or more metals selected from Al, Ga and Cu or an alloy comprisingthe second metal, wherein the alloy material for R-T-B-based rare earthsintered magnets comprises the first metal and the second metal in arange of 0.1 at % to 2.4 at % in total,0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1 wherein Dy represents aconcentration (at %) of a Dy element, B represents a concentration (at%) of a boron element, and TRE represents a concentration (at %) of allthe rare earth elements.
 7. The alloy material for R-T-B-based rareearth sintered magnets according to claim 5, further comprising Si. 8.The alloy material for R-T-B-based rare earth sintered magnets accordingto claim 7, wherein a amount of Si in the alloy material for R-T-B-basedrare earth sintered magnets is in a range of 0.7 at % to 1.5 at %. 9.The alloy material for R-T-B-based rare earth sintered magnets accordingto claim 5, wherein an area ratio of a region including an R₂T₁₇ phasein the R-T-B-based alloy is in a range of 0.1% to 50%.
 10. A process ofproducing R-T-B-based rare earth sintered magnets, wherein the alloy forR-T-B-based rare earth sintered magnets according to claim 1 is moldedand sintered.
 11. The process of producing R-T-B-based rare earthsintered magnets according to claim 10, wherein the sintering is carriedout in a range of 800° C. to 1200° C., and then a thermal treatment iscarried out in a range of 400° C. to 800° C.
 12. The process ofproducing R-T-B-based rare earth sintered magnets according to claim 10,wherein a diffusion step of attaching Dy metal or Tb metal, or a Dycompound or a Tb compound to a surface of a sintered R-T-B-based magnetand carrying out a thermal treatment is carried out.
 13. An R-T-B-basedrare earth sintered magnet comprising: R which is a rare earth element;T which is a transition metal essentially comprising Fe; a metallicelement M comprising one or more metals selected from Al, Ga and Cu; B;and inevitable impurities, wherein R accounts for 13 at % to 15 at %, Baccounts for 4.5 at % to 6.2 at %, M accounts for 0.1 at % to 2.4 at %,T accounts for balance, a proportion of Dy in all rare earth elements isin a range of 0 at % to 65 at %, the following Formula 1 is satisfied,which is made of a sintered body including a main phase primarilycomprising R₂Fe₁₄B and a grain boundary comprising more R than the mainphase, in which the grain boundary phase includes a phase having aconcentration of all atoms of the rare earth elements of 70 at % or moreand a phase having a concentration of all the atoms of the rare earthelements in a range of 25 at % to 35 at %,0.0049Dy+0.34≦B/TRE≦0.0049Dy+0.36  Formula 1 wherein Dy represents aconcentration (at %) of a Dy element, B represents a concentration (at%) of a boron element, and TRE represents a concentration (at %) of allthe rare earth elements.
 14. The R-T-B-based rare earth sintered magnetaccording to claim 13, further comprising Si.
 15. The R-T-B-based rareearth sintered magnet according to claim 13, wherein a volume ratio ofthe phase having a concentration of all the atoms of the rare earthelements in a range of 25 at % to 35 at % is in a range of 0.005 vol. %to 3 vol. %.
 16. The R-T-B-based rare earth sintered magnet according toclaim 13, wherein a concentration of Dy or Tb on a surface of thesintered magnet is higher than a concentration of Dy or Tb in thesintered magnet.
 17. A motor including the R-T-B-based rare earthsintered magnet according to claim
 13. 18. An alloy for R-T-B-based rareearth sintered magnets comprising: R which is a rare earth element; Twhich is a transition metal essentially comprising Fe; a metallicelement M comprising one or more metals selected from Al, Ga and Cu; B;and inevitable impurities, wherein R accounts for 13 at % to 15 at %, Baccounts for 5.0 at % to 6.0 at %, M accounts for 0.1 at % to 2.4 at %,T accounts for balance, a proportion of Dy in all rare earth elements isin a range of 0 at % to 65 at %, a main phase primarily comprisingR₂Fe₁₄B and an alloy grain boundary phase comprising more R than themain phase are included, and an interval between the alloy grainboundary phases is 3 μm or less.
 19. The alloy for R-T-B-based rareearth sintered magnets according to claim 18, further comprising Si. 20.The alloy for R-T-B-based rare earth sintered magnets according to claim18, wherein a ratio (Fe/B) of a amount of Fe to a amount of B is in arange of 13 to
 16. 21. The alloy for R-T-B-based rare earth sinteredmagnets according to claim 18, wherein B/TRE (B represents aconcentration (at %) of a boron element, and TRE represents aconcentration (at %) of all the rare earth elements) is in a range of0.355 to 0.38.
 22. A process of producing alloys for R-T-B-based rareearth sintered magnets comprising: a casting step of casting a moltenalloy comprising R which is a rare earth element; T which is atransition metal essentially comprising Fe; a metallic element Mcomprising one or more metals selected from Al, Ga and Cu; B andinevitable impurities, in which R accounts for 13 at % to 15 at %, Baccounts for 5.0 at % to 6.0 at %, M accounts for 0.1 at % to 2.4 at %,T accounts for balance, and a proportion of Dy in all rare earthelements is in a range of 0 at % to 65 at % using a strip casting methodin which a workpiece is cooled using a cooling roll, wherein, in thecasting step, a temperature-holding step of maintaining a cast alloy ata certain temperature for 10 seconds to 120 seconds while a temperatureof the cast alloy decreases from more than 800° C. to lower than 500° C.is carried out.
 23. The process of producing alloys for R-T-B-based rareearth sintered magnets according to claim 22, wherein the molten alloycomprises Si.
 24. The process of producing alloys for R-T-B-based rareearth sintered magnets according to claim 22, wherein at least a part ofthe casting step is carried out in an atmosphere comprising helium.